No. 74 - December 1993

TELESCOPES AND INSTRUMENTATION

News trom CouncilThe following is Section 1 (the section

relevant for the VLT Project) of the reso­lution issued by Council during its meet­ing of December 2, 1993:

In its October 4 and 5, 1993 meetingCouncil expressed its approval of therevised VLTNLTI project as referred inJune 1993 Cou-483 for content, scheduleand staff. Financial difficulties discussedin the Finance Committee meeting ofNovember 8 and 9, 1993 and recent

expression of concern in a diplomaticnote from the French Government haveled to reconsideration of this plan.

Following the presentation and dis­cussion of different alternatives for costreduction, Council adopts further mod­ifications to the VLT programme plan.This includes the postponement of theimplementation of VLTI, VISA, CoudeTrain and associated adaptive optics forall telescopes. In consultation with the

Scientific Technical Committee a solu­tion will be sought to introduce adaptiveoptics at the Nasmyth foci at the earliestpossible time.

Furthermore, the Executive will en­deavour to reintroduce full Coude andinterferometric capabilities at the ear­liest possible date. This will include pro­visions for continuing technological re­search and development programmesdevoted to this end.

VLT News trom the VLT DivisionM. TARENGHI, ESO

The status of VLT activities is shiftingmore and more from the design to theconstruction phase. Major progress wasachieved in the following areas:

Mechanical Structure

The detailed design of the structure isreaching completion. The calculated low­est locked rotor eigenfrequency is 8.1 Hzaround the elevation axis and about10 Hz around the azimuth axis. To obtainthis and to optimize the manufacturing,

the mass has increased with respect tothe original design. The maximum totalmoving mass is 450 tons which include320 tons of structural steel.

A demonstration test of the encoderwas carried out successfully. This en­coder uses two laser interferometersand a number of flat mirrors fixed onthe structure. Each mirror can cover arange of about 4 degrees and the twoheads permit the transition from onemirror to another without the loss ofinformation.

Enclosures

The design and construction of theenclosures were contracted to theSEBIS Consortium in Italy. The final de­sign is near to completion (January1994).

Wind tunnel tests have been per­formed for the assessment of windloads on a single enclosure. Additionaltests will be performed in November1993 to study the interference betweenthe enclosures.

Mirrors and M1 Unit

The first primary mirror blank hasbeen delivered to REOSC and the padsfor the axial supports have been gluedon the back. The manufacturing of otherblanks by Schott proceeds as planned.Two parallel contracts were issued forthe design of the mirror Gell. The Prelimi­nary Design Review will take place atthe beginning of next year.

M2 Unit

The call for tenders has been issuedand the tenders are expected in mid­December. The requirements include afast guiding mode (field stabilization)and a chopping mode for frequenciesup to 5 Hz and amplitude of up to 1 arc­minute.

Coating Plant

The technical specifications andstatement of work for the Call for Ten­ders have been completed. The specifi­cations are based on a sputtering pro­cess. The start of the contract is ex­pected to be May 1994.

Washing Unit and Cleanroom

The specifications and statement ofwork for the call for tenders is beingprepared. The contract for the washingunit will include the pilot washing unit(for the 3.6-metre mirrors) for La Silla.Cleanroom specifications have beenprepared. The cleanroom will compriseboth the coating and washing unit forthe 8-m mirrors.

Cassegrain and NasmythAdapters

The conceptual design has beencompleted and the call for tenders willbe sent out early in 1994 after analysis

of the results of a preliminary enquiry. Acall for tenders is running for the pro­curement of CCD cameras for autoguid­ing and wavefront sensing applications.

Coude Station

The concept is based on a large turn­table on which all the coude stationequipment is fixed. It is used to com­pensate the field rotation for coude in­struments and to position the collimat­ing units to be used for the differenttypes of beam combinations. The con­tract for the construction of turntableshas been issued.

Adaptive Optics

An optimization study has permittedthe finalization of the essential parame­ters necessary for the establishment ofspecifications.

Handling Aspects

A new concept for the M1 handlingtool has been developed. The principleis a hydraulic whiffle tree. The geometryis identical to that of the REOSC tool.The M1 handling tool will include thelifting system and will form a self-stand­ing unit in the Mirror MaintenanceBuilding.

VLTI System Level

A number of studies at system levelare currently being carried out or havebeen completed. These studies are im­portant for assessing the overall perfor­mance of the VLTI as weil as for thespecification of VLTI subsystems, suchas the delay lines. Studies include:

- Control model of delay line/fringesensor

- Structural deformation of unit tele­scopes under wind loads

- Study of acoustic noise inside UT en­closures

- Study of thermal environment in VLTIfacilities

- Measurements of ground transferfunctions on Paranal

Auxiliary Telescopes

Calls for tenders for the design,manufacture, test in Europe, transportto and erection in Chile of three auxiliarytelescopes and equipment for 11 sta­tions were sent to industry in July 1993.

Beam Combiner System

An in-house design study of the beamcombiner is nearing completion. Themain objective of the study is a concep­tual design which allows the assessmentof the interface to the civil engineeringinfrastructure and understanding of thetradeoffs between various concepts forthe homothetic mapping.

Instrumentation

The VLT Medium Resolution Spec­trometer/lmager (ISAAC) reached the Fi­nal Design Review (FDR). The CONICA(High Resolution Near Infrared Camera)and FORS (Focal Reducer Spectro­graph) are approaching the FDR stage.The UV-Visual Echelle Spectrograph(UVES) completed the Preliminary De­sign Review in October. The Multi-FiberArea Spectrograph (FUEGOS) is beingstudied by a consortium composed ofthe Observatoire de Meudon, the Ob­servatoire de Geneve, the Observatoirede Toulouse and the Osservatorio diBologna. The Phase A study ended inOctober and is being reviewed by ESOtechnical staff. The Mid-Infrared ImageSpectrometer is being studied by theService d'Astrophysique CEAlDAPNIAand is making progress in Phase A.

First Light from the NTT InterferometerT.R. BEDDING, 0. VON DER LÜHE andAA ZIJLSTRA, ESOA ECKART and L.E. TACCONI-GARMAN, MPE Garehing, Germany

It is not obvious that placing a maskover a telescope and blocking most ofthe light will improve its imaging perfor­mance. Yet several groups have donejust this in an effort to overcome thelimits of atmospheric seeing andachieve the best angular resolution fromlarge telescopes such as the 4.2-mWHT, the 3.9-m AAT, the Haie 5-m andthe Mayall 4-m at Kitt Peak. Aperture

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masking has mainly been used for brightsources having reasonably simple struc­ture. Fortunately, there are some veryinteresting objects that satisfy thesecriteria: cool giant stars, whose largeangular diameters (up to -0.05") makethem ideal targets for big telescopes.Aperture masking has so far alloweddetection of convective hot spots on thered supergiant a Ori and asymmetries in

the atmosphere of Mira (e.g., Wilson etal. 1992; Haniff et al. 1992).

This article describes aperture-mask­ing observations of cool giants with the3.5-m ND in the near infrared (1.5 ~lm).

We chose the infrared because, al­though the angular resolution is some­what poorer than at visible wavelengths,the stars are much brighter and the at­mospheric seeing is more favourable.

Before describing our observations, wegive abrief introduction to the tech­niques involved.

Optical/IR Interferometry

To produce images that have highangular resolution one must overcomethe seeing. This means compensatingfor perturbations in the wavefront of thelight that result from its passage throughthe atmosphere. These perturbationsarise because the refractive index of theatmosphere is continually fluctuating,primarily due to turbulent mixing of re­gions of air with differing temperatures.The incoming wavefront can be thoughtof as being made up of a large numberof patches, each having a diameter of ro,where the wavefront is approximatelyflat across each patch. The quantity rodetermines the seeing: at a wavelengthA, the seeing disk has a FWHM of about1.2 Vro (e.g., ro = 15 cm at 550 nm for 1"seeing).

Adaptive optics seeks to compensatefor wavefront perturbations in real timeusing a small deformable mirror. Pro­vided the mirror has enough actuators(one for every ro-sized patch on thepupil), it is possible to place most of thelight in a diffraction-limited core. Ofcourse, one also requires sufficientphotons per ro-patch to measure thewavefront and calculate the correction.'

It is possible to achieve high angularresolution passively (i.e. without adap­tive optics), provided one has a fastdetector. This involves recording thedistorted image in a succession of shortexposures, each of which "freezes" theseeing, and processing them off-line.This is the basis of speckle interferome­try. Each short-exposure image con­tains high-resolution information whichcan be extracted via a Fourier transformand calibrated using similar observa­tions of a nearby unresolved star.

Aperture masking is identical tospeckle interferometry, except that oneplaces a mask over the telescope pupil.The mask may consist of a smallnumber of holes arranged in a non-re­dundant pattern (i.e., so that all baselinevectors are distinct). Alternatively, it maybe partially redundant, such as anannulus or a slit. The pros and cons ofaperture masking have been discussedelsewhere (Haniff & Buscher 1992;Buscher & Haniff 1993; Haniff 1993) andhere we simply try to summarize themain arguments.

1 Adaptive optics is not lhe same as active optics.The lalter involves adjusting the primary mirror 10correcl tor lelescope f1exure, etc., and the correc­tions are necessarily made on a much slowertimescale. This type or correction produces excel­lent long-exposure images, but cannot be used torreal-time seeing compensation.

Why Use an Aperture Mask?

Each ro-sized patch on the pupil hasan unknown phase error, correspondingto the unknown thickness of atmo­sphere above it. Each pair of patchesforms an interferometer that measures aparticular spatial frequency on the sky.With an un-masked pupil there are manydifferent pairs measuring a given spatialfrequency. Each one contributes a dif­ferent phase error, so that many fringepatterns with the same spatial frequen­cy are superimposed on the detectorwith different position offsets. The resul­tant fringe power will be the sum ofthese randomly-phased contributions.The problem is that the wavefront errorsare different in every short-exposure im­age, so the final fringe power, being thesum of a random walk, will also fluctu­ate. This introduces so-called atmo­spheric noise in the power spectrum. Anon-redundant aperture mask, in whichno baseline is sampled more than once,eliminates atmospheric noise. This isparticularly important in the infrared,where the large numbers of photonsmean that atmospheric noise usuallydominates over photon noise.

Another advantage of non-redundantaperture masking is that it improves theaccuracy with which one can correct forvariations in atmospheric seeing, some­thing which is often the limiting factor inhigh-resolution imaging. This is becausea pupil composed of subapertures eachhaving size :s ro is quite insensitive tochanges in the actual value ro. Ofcourse, a mask also reduces the lightlevel and restricts observations to brightobjects. But for those objects, there isan additional advantage if the light beingdiscarded does not carry useful infor­mation. This last point becomes clear ifone imagines observing an object wh ichis only barely resolved by the full tele­scope aperture. In this case, the "useful"light comes from the outer parts of thepupil and the remainder only serves toadd noise to the signal we are interestedin. By using a mask, one can effectivelyincrease the resolving power of the tele­scope by giving more emphasis to highspatial frequencies.

A big drawback of using a non-redun­dant mask with a small number of holesis the poor coverage of spatial frequen­eies. A good compromise in the photon­rich infrared regime is an annular mask.This has full spatial frequency coveragewhile being minimally redundant: rough­Iy speaking, each baseline is measuredtwice. Furthermore, a thin annulus large­Iy retains the other advantages men­tioned above, namely accurate calibra­tion and enhanced resolution. However,an annular mask is not a good choice inthe visible regime, where photon noise

Figure 1: To change between masks, the NTTwas tilted to 15° (rom the horizontal and themirror cover (grey) was partially closed. Here,Oskar von der Lühe (Ieft) and Tim Bedding(right) stand on the telescope structure andshow off the 7-hole mask. The black circlebehind their heads is the annular maskattached to the M3 baffle. Andreas Eckart isstanding at floor level.

generally dominates over atmosphericnoise. Here, Buscher & Haniff (1993)advocate the use of a long slit.

We do not wish to give the impres­sion that masking a telescope is alwaysthe best strategy. In same situations,however, there are powerful argumentsfor doing so and these issues are dis­cussed more fully in the references. Tosummarize, an aperture mask with non­redundant holes provides more accu­rately calibrated measurements at thefull diffraction limit, but at the expense oflower sensitivity and poorer spatial-fre­quency coverage. As noted above, anannular mask should be a good com­promise in the infrared, but this methodhas so far only been tested on binarystars (Haniff et al. 1989).

Masking the NTT

Our observations were made on theND in August 1993, using the SHARPinfrared camera (Eckart et al. 1991). Inorder to sampie the images fully at thediffraction limit at the J band, it wasnecessary to magnify the image scale.We did this by placing a focal expanderjust in front of the dewar window. Thisdevice, wh ich we named COSHARP,consisted of a pair of lenses mounted inan aluminium tube. COSHARP per­formed perfectly and we wish the samesuccess to its more expensive space­based cousin.

3

•

1Il tl

~, ~ fl e., ..l!I f, e e .. 1,; '" 6

'" •ft @> & 0 l!I l!I ~

& '"tl e +) • • I!' e l!I

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• .,

"Ii

.. ... •• •, "' ..

..•

• •111 .I!l ...... .'. .~.. ....

• • m' •.. .• •• I

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Figure 2: (a) The 7-hole non-redundant mask, with the pupil of the NTT shown as dashed eire/es, (b) Theoretical spatial-frequency coverage. Thecentral red dot is the origin and the other points (in symmetrical pairs) show the 21 different baselines.(c) Typical 0.1-s exposure of a bright star. The envelope corresponds to the airy disk of a single hole and fringes from the interferometric arrayare clearly visible. The image is 2.9" across.(d) The average power spectrum of 200 interferograms like the one in (c). Since the telescope has an alt-azimuth mount, the orientation of thepattern varies with the rotation angle of the mask with respect to the sky.

We observed several red giants andMira variables using both an annularmask and a 7-hole non-redundantmask. Placing a full-sized mask over theprimary mirror of a large telescope israther difficult, especially if you want tochange between different masks duringthe night. The solution adopted by mostobservers is to place the mask insidethe instrument at an image of the tele­scope pupil. Re-imaging the pupil to adiameter of -20 mm with a lens allowsone to use a correspondingly smallermask, wh ich is very convenient but re­quires extra optics to be inserted in thesystem. With SHARP on the ND, thiswas not practicable.

The ND is a compact alt-azimuth te­lescope in a small enclosure, making itquite easy to access the telescopestructure. This allowed us to place themasks on the baffle in front of Mirror 3,at wh ich point the converging f/11 beamhas a diameter of 45 cm. The maskswere made from 5 mm thick black PVCand, by bolting a mounting ring to theM3 baffle, we were able to attach andremove them very easily. To reach theM3 baffle, we drove the telescope to its

lowest elevation (15°), partly closed theprimary mirror cover and climbed ontothe telescope structure. The whole pro­cess of changing the mask took twopeople about 5 minutes (see Figure 1).

The mirror cover of the ND opens likea pair of sliding doors, wh ich makes ituseful as a secure handhold. We note inpassing that this mirror cover can easilybe used to create a slit mask, simply byopening the cover to the desired width.As mentioned above, a slit mask can beused for interferometry at visiblewavelengths.

The design of the 7-hole mask isshown in Figure 2 (a). When projectedon the entrance pupil of the ND, theholes have a diameter of 25 cm and lieon a circle of diameter 3.05 m. We didnot use the full diameter of the pupil(3.5 m) in order to avoid vignetting thatwould arise from the mask not beingexactly at the pupil plane. Figure 2 (b)shows the two-dimensional spatial fre­quency coverage. The arrangement ofthe holes is based on a design by Corn­weil (1988), except that we moved thelower pair of holes closer together tomake the radially-averaged coverage

of spatial frequencies more uniform.Figures 2 (c) and (d) show data from abright star. The signal in the powerspectrum is attenuated relative to thetheoretical pattern (2 b), mainly due toseeing decorrelation during each 0.1-sexposure. This exposure time, whichwas set by the detector system, is a littlelong and we plan to install a fast shutterfor future observations.

The annular mask (Figure 3) has aneffective outer diameter of 3.3 m and awidth of 20 cm. The transfer function(Figure 3 b) gives strong emphasis tohigh spatial frequencies. In the mid-fre­quency range the transfer function is afactor of -7 below that of the unmaskedtelescope. However, in the presence ofseeing, the signal from the unmaskedtelescope is strongly attenuated, whilethat from the annular mask (Figure 3d)is less severely affected.

Results and Future Prospects

Despite poor weather, we obtainedgood observations of several southernred giants and Miras that we would ex­pect to have large angular diameters.

02 0<4 06 08Angular frequcrlcy

Figure 3: (a) The annular mask, with the pupil of the NTT shown as dashed eire/es.(b) Radial cuts through the NTT modulation transfer function in the absence of seeing effects. The solid curve is for the annular mask and thedashed curve is without a mask (but including the telescope's central obstruction). An angular frequency of 1 corresponds to the diffraction limitof the fu/l 3.5-m aperture.(c) Typical O. 1-s exposure of a bright star, showing many sma/l speckles. The image is 2.9" across.(d) The average power spectrum of 500 interferograms like the one in (c). The origin of the spatial frequency domain is at the centre, where thesignal is strongest. The arc-like features are due to the telescope spiders and also to a deposit on M3 courtesy of the bird life on La Silla.

4

Preliminary analysis of the data indi­cates that these stars are resolved andthat they probably rival Betelgeuse andMira in angular size. If this turns out tobe the case, we will be able to look forevidence of asymmetries and surfacefeatures on these stars.

The number of stars that can be re­solved by 4-m-class telescopes is smalI,but the results so far have proved veryinteresting. The new generation of8-10-m telescopes will give a big im­provement in angular resolution, andmasking observations similar to thosewe have described should allow de­tailed study of stars with large angulardiameters. At the moment, however,

there are always practical difficultieswith aperture masking. We thereforehope that future instruments will be de­signed to contain a reimaged pupil atwhich masks can be easily inserted.

We thank Reiner Hofmann for makingCOSHARP, Gerardo Ihle and the staff inthe La Silla workshop for making themasks, and telescope operator Francis­co Labrafia for excellent support duringthe observations.

ReferencesBuscher, D.F., & Haniff, CA, 1993, J. Opt.

Soe. Am. A. 10, 1882.

Cornwell, T.J., 1988, IEEE Trans. Antennasand Propagation 36, 1165.

Eckart, A., Hofmann, R., Duhoux, P., Genzel,R., & Drapatz, S., 1991, The Messenger65,1.

Haniff, CA, & Buscher, D.F., 1992, J. Opt.Soe. Am. A. 9, 203.

Haniff, CA, Buseher, D.F., Christou, J.C., &Ridgway, S.T., 1989, MNRAS 241, 51 P.

Haniff, CA, Ghez, A.M., Gorham, P.W, Kul­karni, S.R., Matthews, K., & Neugebauer,G., 1992, AJ 103, 1662.

Haniff, CA, 1993, Speckle v non-redundantmasking. In: Robertson, J.G., & Tango,WJ. (eds.), Proe. lAU Symp. 158, VeryHigh Angular Resolution Imaging, Sydney,Australia, January 1993, in press.

Wilson, R.W, Baldwin, J.E., Buscher, D.F., &Warner, P.J., 1992, MNRAS 257,369.

Optical Gyro Encoder Tested on the NTTH. OAHLMANN, B. HUBER, W SCHRÖOER, L. SCHÜSSELE, H. ZECH, Fachhochschule

Offenburg and Steinbeis Transfer Zentrum Physikalische Sensorik, Offenburg, GermanyM. RAVENSBERGEN, European Southern Observatory

The optieal gyro eneoder mounted on the NTT eentre pieee (altitude axis). The ring laser withits front-end eleetronies is mounted in the box, while the fiber gyro is mounted on the right­hand plate. Dimensions of the mounting box are about 45 x 45 x 45 em. The axis of the optiealgyro eneoder is from left to right on this pieture.

The prototype of the optical gyro en­coder (see [1] and [2]) has been suc­cessfully tested on the ND telescope inthe period of 5 to 10 September 1993.Day time tests until 20 Septemberproved the repeatability of the measure­ments. The tests confirmed the specifi­cations of the encoder and qualified thistype of angular encoder for the use in anoptical telescope.

The optical gyro encoder (OGE) con­sists of two gyros:1. A ring laser gyro. This gyro consists of

a triangular or square light path withmirrors in the corners. Laser light froman ionizing laser source (e.g. HeNe) isemitted in the 2 directions of the lightpath and the resulting interferencepattern is measured.The light path is made in a glass blockwith a thermal expansion coefficientof zero. It has therefore a very stablescale factor but the resolution is notsufficient.

2. A fiber optic gyro. This gyro consistsof a polarization maintaining fiber,which is wound on a coil. A lightsource emits light in the two direc­tions of the coil, and the interferencepattern is measured. Compared witha ring laser gyro with the same en­closed area for the light path, the sen­sitivity multiplies with the number ofturns. This results in an excellent res­olution and low noise. 'On the otherhand, the scale factor is not sufficientbecause of imperfections in the opti­cal elements and thermal effects.

In principle, the OGE integrates thesignal of the ring laser gyro and com­pensates it for misalignments and earthrotation in order to get the angles intelescope coordinates. The ring lasergyro data are also used to stabilize thefiber optic gyro. The data collection washowever done for the two gyros indi­vidually and the data were evaluated off-

line in order to find the best integrationtime constant.

The OGE data were transformed intoaltitude/azimuth coordinates accordingto its system equations and calibrationdata. This was compared with the read­ings of the altitude and azimuth encod­ers of the ND.

The OGE was first mounted on the

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azimuth box to measure azimuth rotationand was later fixed to the centrepiece inorder to measure altitude rotation.

The OGE measures in respect to iner­tial space, while the NTI encodersmeasure in respect to altitude/azimuthcoordinates of the earth frame. Becauseof this basic difference in operation,several special effects were detected:1. Stressing of the azimuth bearing

support ring. When the telescopestarts to move from a stand-still posi­tion, the telescope is already movingbefore the NTI encoder measures arotation. This is due to the friction inthe radial bearing of the azimuth axis,which is also the mounting location ofthe NTI encoder.

2. Sag of structural parts of the center­piece of the NTI according to thealtitude position.

3. Minor nonlinearities of the NTI en­coders in the sub arcsec range.

4. Details of the control loop behaviour.

The preliminary evaluation of the testdata gave the following characteristics:Pointing accuracy: Azimuth axis:

< 0.7 arcsec rmsAltitude axis:< 1 arcsec rms

Tracking accuracy: < 0.1 arcsec rmsover a time of 30 seconds

Resolution: < 3 x 10-4 arcsec at a read­out rate of 10Hz

Bandwidth: up to 120 Hz (adjustable bysoftware)

No temperature compensation had tobe applied.

In gyro terms the data are as folIows:Bias stability: < 2 x 10-3 degrees/hourScale factor stability: < 1 ppmRandom walk coefficient: < 5 x 10-4 de­

greesl our.

The high resolution and bandwidthmake the OGE an excellent device fortelescope tracking. Having fiber opticgyros mounted on the telescope tube,the rotation rate has to be zero duringtracking for alt-azimuth mounted tele­scopes as weil as for equatorialmounted telescopes. However, the in­trinsic integration principle and drift re­quire the use of an initialization refer­ence and an autoguider.

The installation of an OGE is easy be­cause it does not need to be mounted inthe telescope axis and there are no tightmechanical tolerances to be respected.

On an equatorial mounted telescope,the application is even easier becauseno coordinate transformation is needed:If one OGE is mounted on the alpha andanother one on the delta axis, they seean inertial rate of zero during tracking.

This also means that, in this case, thetracking performance is not dependenton a pointing model: the OGEs drive themotors in such a way that the inertialrate becomes zero.

The test campaign proved that thisdevice is also quite useful for calibratingexisting encoders and for analysing ex­isting telescope control loops and struc­tures.

Acknowledgement

The authors would like to thank:- the personnel of ESO in Chile for their

support in the preparation and theexecution of the test,

- B. Gilli from ESO Garching for thepreparation of the software on theNTI,

- the co-workers at the Fachhochschu­le Offenburg and the STZ Physika­lische Sensorik for their excellent de­velopment work and

- the Ministry for Research and Tech­nology of Baden-Württemberg.

References[1] F. Merkle and M. Ravensbergen: The

Messenger No. 65, Sept. 1991.[2] W. Schröder et al. (1991): Proc. SPIE

1585.

Infrared Astronomy with Arrays: the Next GenerationA. MOORWOOO and G. FINGER, ESO

The title is that of a conference held atUCLA in July 1993 at which approxi­mately 250 participants experienced afeast of 73 papers and 120 posters cov­ering both recent astrophysical resultsand future prospects for the next gener­ation of infrared array instruments onlarge ground-based telescopes and inspace. Although it was a very excitingmeeting both scientifically and techni­cally with many highlights, the purposeof this article is not to review the confer­ence (to be published as a book byKluwer and edited by lan McLean) but todraw attention to developments in thefield of infrared array detectors reportedthere which are of great interest for bothplanned and future VLT instruments.Partly because the conference wasin California, the infrared detectormanufacturers were represented inforce to present their products and sol­icit feedback from users on the perfor­mance of current arrays and their futurerequirements in a special "meet the in-

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dustry" evening session. Such sessionshave become a regular feature ofspecial ist infrared conferences, and thisone really demonstrated the extensivecooperation which has developed be­tween astronomers and industry duringthe last few years and the remarkableprogress made in the developmentlop­timization of arrays for infrared as­tronomy.

Based on the quantity and quality ofthe scientific results presented, thestandard in the near infrared (1-2.5Ilm)region has ciearly been set during thelast few years by the 256 x 256Hg:Cd:Te NICMOS3 array developedfor the HST instrument with whosename it has become synonymous (andwhose home was visited by many of theparticipants on an oversubscribed tourorganized by the RockweIl InternationalScience Center). This is the array in­stalled in IRAC2 atthe 2.2-m telescope onLa Silla and currently baselined for theshort wavelength channels of the ISAAC

(see The Messenger, 70, 10) and CONI­CA (The Messenger, 67, 17) instrumentsfor the ESO VLT. With its relatively shortlong wavelength cut-off this array yieldsextremely low dark current (-0.1 eis)and read noise (-20e) at comfortableoperating temperatures -70K. Resultsat the conference, however, revealedthe strong competition it now faces fromthe new SBRC 256 x 256 InSb array,successor to their famous 58 x 62 de­vice, which is sensitive out to 5 ~lm andhas been baselined for the longwavelength channels of ISAAC andCONICA. Somewhat unexpectedly, thefirst tests of these arrays have shownthat they can also compete with theHg:Cd:Te arrays with regard to dark cur­rent and noise, albeit at less comfort­able temperatures (-30K) and withmuch more stringent requirements onthe instrumental background due totheir longer cut-off wavelength. Theyalso yield quantum efficiencies >0.8which are higher than the Hg:Cd:Te

arrays at the short wavelengths and donot appear to suffer from the persist­ence and "glow" problems of thesearrays under extremely low backgroundconditions. Among the first instru­ments equipped with such an array isthe Caltech infrared camera for the Kecktelescope which has already achieved a1a K' (2.1 /-lm) limit of 22 mag./sq. arc­sec in 20s of integration time. Unfortu­nately, the weil capacities of the firstdevices are rather low (-2·1Q5e) forground-based L (3.8 /-lm) and M (4.8/-lm)broadband imaging. At ESO, however,we are currently preparing to test anengineering array of this type and ex­pect delivery early next year of a sciencegrade array with higher weil capacity ifcurrent experiments with higher dopingat SBRC are successful. CincinnatiElectronics also presented their new256 x 256 InSb array which yields higherweil capacities of -106e at the expenseof higher dark current and read noiseand could be of great interest for long­wavelength imaging. The big news,however, was that both Rockweil andSBRC have now started development of1024x 1024 arrays, i.e. jumping the pre­viously anticipated next step in format.Both plan to utilize four quadrant read­out chips so that 512x512 arraysshould also be available if required andoffer a fallback if yield of the full arraysproves to be a major problem. Bothcompanies appear to be more con­cerned, in fact, by yield (and hence cost)than technical performance aspects al­though Rockweil plan a concertedattack on the persistence problem andhope also to increase quantum efficien­cy and reduce the read noise of the newdevices to -5e. The prospect now,therefore, is not only of much larger

formats but also improved sensitivityand hence a considerable overall perfor­mance gain. One of the VLT infraredinstruments still in the definition phaseat ESO - the cryogenic infrared echellespectrometer - actually requires arraysof this size for a reasonable echelle for­mat and will c1early profit from any im­provement in noise performance assuch an instrument should be detectorlimited over much of its wavelengthrange. Technically, it is also not too lateto plan for the use of these larger formatarrays in ISAAC and CONICA. Althoughthe present 256 x 256 arrays werebaselined even before these arrays be­came commercially available, the opti­cal designs of both instruments werespecified to accommodate 512x512arrays in anticipation of future develop­ments. An expansion to 1024x 1024now appears possible without major op­tomechanical changes if and when theybecome available.

Considerable progress was also re­ported on the development of longerwavelength arrays which cover the 10and 20/-lm atmospheric windows andare of interest for the VLT mid-infraredimagerlspectrometer for wh ich ESO hascontracted a Phase A study to a consor­tium of institutes led by the Serviced'Astrophysique, Saclay (see TheMessenger, 73, 8). Performance of thehigh weil capacity (-107e) 64x64 Ga:Siphotoconductor array developed byLETI/L1 R in France for ground-baseduse in the 10/-lm window was demon­strated to good effect by an image of theß Pic disk obtained by P.O. Lagage us­ing TIMMI at the ESO 3.6-m and votedone of the conference scientific high­lights by Mark Morris in his closingsummary. The follow-on development of

this device to a format of 128x 192 pix­els being managed by INSU and withESO participation was also presented. Anovel feature of this array, appreciatedby many participants, is the possibilityof switching between high and low val­ues of the charge capacity in order tooptimize its performance under differentbackground conditions (e.g. imagingand spectroscopy). Both SBRC andRockweIl have also developed low­noise, high-capacity (107e), As:Si IBCIBIB (Impurity Blocked ConductionlBlocked Impurity Band) arrays with for­mats up to 256 x 256 which are sensitivethroughout the 10 and 20flm windowsalthough it has yet to be established thatsuch devices can be exported outsidethe United States. RockweIl also re­ported progress with As:Si solid-statephotomultipliers which have high q.e.'s(-0.7) and are capable of counting sin­gle photons with a response time of50ns. Although the present formats aresmall (10 x 10), these devices may be ofinterest in the future for very lowbackground (e.g. high-resolution spec­troscopy) applications and the measure­ment of fast transient phenomena.

This is obviously an exciting andprobably exceptional period in the his­tory of infrared array development. If, asexpected, the detectors highlightedhere materialize within the next fewyears, infrared astronomers will haveevolved from using noisy single detec­tors to almost "perfect" arrays of onemillion pixels within aperiod of littlemore than a decade. Coupled with thenew instrumental opportunities createdand the larger telescopes now underdevelopment, they will clearly open theway for the next big step in our explora­tion of the infrared universe.

Current CCD Projects at ESO and Their Relation to theVLT Instruments0. IWERT, ESO

1. Introduction

The following is abrief description ofCCO detectors foreseen to be used withVLT instruments currently under studyor design and of the contracts underway to procure them.

In the actual sequence of work, therequirements on the detectors to beused are set in the instrument designphase and this is the starting point forthe procurement activities. In this pre-

sentation, it is more convenient to de­scribe the various developments nowunder way and then state their relevanceto the different VLT instruments.

Oifferent strategies of procurementare necessary because large CCO de­tectors for application in advanced as­tronomical instrumentation are not avail­able as off-the-shelves products.Moreover it is not possible to define astandard CCO device, because the re­quirements change from instrument to

instrument depending on its scientificaim. One can differentiate between thefollowing types of CCOs:• Well-specified "catalogue products"

where a design and manufacturingprocess already exist and the deviceis to a basic extent tested at themanufacturer. For large sizes, how­ever, the manufacturing itself still im­plies a number of risks (e.g. in thin­ning) thus making the delivery un­foreseeable.

7

Table 1: Summarized Specification for the main parameters of the thinned Thomson 20482,

15-llm Pixelsize devices

PARAMETER GUARANTEED PERFORMANCE

•CHIP TOPOLOGY

Operation mode Frame transfer, single fieldReadout mode - At least two identical on-chip output amplifiers on

one chip side offering the possibility of simultane-ous readout to reduce the overall readout time

- The entire charge pattern of the light sensitivearea may be read through either one of thoseoutput amplifiers or simultaneously through all ofthem, if so required

•GEOMETRICAL CHARACTERISTICS

Pixel size 15 micron square format100 % aperture

Pixel number 2048 x 2048

•MECHANICAL CHARACTERISTICS

Flatness of light sensitive area 15 mieren peak to peakPackage and Chip design Three-side buttableDead surface gap Less than 400 mieren between sensitive areas

(mounted in TMS package) of the specified CCDs

•ELECTRICAL PERFORMANCE

Readout noise in slow scan operation Less than 4e- (target): 10e- (upper limit) at Data rate50 KHz with C.D.S. measurement performed at-40·C

Full weil capability More than 100000e- measured at -80·C(Design goal 130000el

Charge transfer efficiency per clock Better than 0.99995 measured at -80·Ccycle (Design goal 0.99999)Dark Current (D.C.) Less than 0.1 e-/min/pixel at -80·C

Measurement performed at +20·C:D.C. (-80·C) = 3.10-6 x D.C. (+20·C)

Additional Features Binning facility for 2 x 2 pixels with full signal (designgoal)Nominal operating mode is MPPEither Inverted or Non-inverted mode operation ispossible

•OPTICAL PERFORMANCE

Quantum efficiency > 20 % at 350 nm (design goal: 30 %)> 45 % at 450 nm (design goal: 50 %)> 60 % at 600 nm> 25 % at 900 nm (design goal: 30 %)All QE values measured at -80·C

Uniformity of QE across light sensi- Within 30 % peak to peak over the whole lighttive area sensitive area

Typical value of High Frequency Photo ResponseNon Uniformity: ± 3 %Measurement at -80·C

Cosmic Ray Sensitivity <3 events/(cm2• minute) at a CCD temperature of

-80·CDefects Not more than 10 bad columns

Less than 500 hot or dark pixels

• Oevices on a best-effort contract withdetailed specifications but withoutmanufacturer's guarantee to meetthem and mostly without anymanufacturer's involvement in devicetesting and characterization.

• Unique prototypes to test new de­velopments which, when successful,can lead to the definition of new cata­logue products.

It will be impossible to describe andcompare all parameters of the variouseeos here, so that this article is focus­ing on the physical device format, pixelsize, buttability, number of outputs,thick or thin version, the latter being thefundamental requirement to reach highquantum efficiency over the spectralrange from UV to NI. The performance inread-out noise, weil capacity, uniformi­ty, etc. is equally important but wouldrequire a detailed discussion which isoutside the scope of this article. Therelevance of these parameters changealso very much depending on thespecific, astronomical application theyare intended for.

2.20482 , 15-flm Pixel Size CCOstram Thomson TCS

Based on scientific requirements forcurrent and future instruments, all mainparameters of a eeo were set up in abaseline specification in November1991 to look for a supplier being able toaccept certain risks in the developmentof a thinned product of the required size.

After a formal call for tender proce­dure, Thomson TeS, Grenoble, wasselected in June 1992 for the develop­ment of this product. The intention wasto establish a specified product beingcharacterized almost completely by themanufacturer himself, thus providing a"standard" product with guaranteedperformance.

The specifications were developed inco-operation of ESO and TeS as atrade-off between scientific require­ments and technical solutions - risksthe manufacturer could accept in termsof predictability, yield and accuracy. Theresult is the product Thomson THX 7397M, which - assuming the developmentis successful - is intended to be offeredalso to other customers.

It features a 20482 detector with15-f.l.m pixel size, 3-side buttable, twooutputs and will be thinned with subse­quent surface treatment not requiringUV flooding for optimal operation. Thespecifications are summarized inTable 1.

A number of mechanical/electricalsampies and an engineering grade areto be delivered until January 1994followed by the final delivery until

8

May 1994 of five devices fully meetingall specifications.

Figure 1 shows a first frontside illumi­nated (thick) sampie shown in thecourse of the eeo workshop 4/5 Oc­tober in Garching. Looking at the photo­graph you might notice the rather un­conventional package construction ofthe eeo, attempting to implementmechanical requirements for mosaick­ing right from the design start with mini­mal mechanical adjustment needs.

The final use of these detectors isforeseen at the echelle spectrographs(UVES) under construction for the Nas­myth foci of the VLT. One of the instru­ment configurations under study isbased on the use of a 3 x 1 mosaic. If themanufacturing is successful, these de­vices could also be used to upgradeLa Silla instrumentation and be im­plemented in second-generation VLT in­struments. A mosaic of 2 x 2 devices ofthis type can also be considered as a

backup solution for the Focal Reducerspectrographs for the VLT (FORS1 andFORS2).

3. 20482, 24-f..lm Pixel Size eeos

trom SITE

The CCO department of Tektronixwas sold in November 1993 to SITE (=Scientific Imaging Technologies), awholly owned subsidiary of CBA Int.Three "catalogue" devices TK2048EBfeaturing 20482 format, 24-flm pixelsize, non buttable, 2 (4) outputs,thinned, not requiring UV flooding are onorder. The possibility to apply a specialUV coating to even improve the quan­tum efficiency of the thinned CCO main­Iy between 300-350 nm is still investi­gated but, as a drawback, would requireUV flooding. As this is a "catalogue"product, the devices are characterizedpartly by SITE.

The final use is foreseen at the redcamera of EMMI at the ND and theFocal Reducers at the VLT (FORS 1and 2).

The delivery of these devices is cru­cial, since EMMI red has been waitingfor it for a number of years, thus operat­ing presently at only 50 % of theforeseen efficiency. Envisaged deliverydates are January 1994, January 1995and July 1995 but may change so thathere the establishment of a reasonablebackup solution is necessary.

Figure 1: The first-front side sampie of the described Thomson 20482 GGO during inspeclion atESO (Ieft), tagether with a "package sampie", i.e. the support without the chip (10wer right). Aview of the sampIe almost face-on is shown in the insert.

4. 20482 Format, 15-f..lm Pixel Sizeand 20482 Format, 24-f..lm PixelSize eeos trom LORAL South

In order to establish a backup solutionfor devices of 2K format with 15-flm pixelsize, a foundry run of an existing designwas ordered in June 1993 at LORAL. Thedesign of this device was done by JohnGeary, Harvard Smithsonian Inst., andhas the following main characteristics:20482 detector with 15-flm pixel size,3-side buttable, two outputs. Oevicesproduced by LORAL are thick devicesand can at LORAL only be enhancedwith lumigen coating (not requiring UVf1ooding). As a consequence, thequantum efficiency in the blue is poorand could be improved by means ofthinning and surface treatment. In thiscase the foundry approach basically de­livers only the processed wafers of whichby preliminary tests aselection of theCCOs must be done for frontside (thick)packaging, lumigen coating or for laterthinning as described in the next para­graph. No device characterization orpackaging solution for buttability isoffered by the manufacturer, so that thecustomer has to find his specific solu­tion. Oelivery of the raw wafers isforeseen at the beginning of 1994.

Figure 2 shows another custom de­sign of a special CCO under way atLORAL for ESO since April 1993. It fea­tures the following characteristics: 20482 ,

24-flm pixel size, 4 outputs, non buttabletogether with the following trackerCCOs on the same chip: 2 guidingCCOs of format 180x200 active imag­ing zone, 24-~lm pixel size, 1 output and2 guiding CCOs of format 180x400 ac­tive imaging zone, 24-flm pixel size, 1output. Here the design was partly doneby LORAL and partly at ESO in-house ina very flexible co-operation. Again thedevices are thick and solutions for pack­aging, testing, enhancement, etc. haveto be provided by the customer. TheseCCOs are intended to be mounted in thetwo direct CCO cameras which areforeseen as testing devices for the opti­cal quality and the operation of the VLTUnit Telescopes. The field covered bythe scientific CCO corresponds to ap­proximately 1.5 x 1.5 arcmin. Besidesthe standard readout, the CCO willbe used in 2 x 2 or 4 x 4 binned mode(pixel size 0.08 and 0.16 arcsec respec­tively).

Other possible uses of the devices areto serve as a backup solution for the

CCOs of the FORS instruments (singleuse of the scientific CCO) and to beused for tests of the improvements inimage quality by rapid guiding with oneof the four small frame-transfer CCOsaccommodated at the four corners onthe same die (i.e. wafer substrate) as thescientific CCO (Figure 2). Oelivery of theraw wafers is envisaged for March 1994.

5. eeo Thinning at Steward Ob­servatory, University ot Arizona

The group led by Mike Lesser at theSteward Observatory has been workingextensivelyon the actual thinning pro­cess and surface treatment for about10 years and demonstrated very prom­ising results in 1992 with the thinning ofLoral South CCOs. Although being ca­pable of reaching high quantum efficien­cy, the devices do presently require UVf100ding as the surface treatment is nota permanent solution in terms of theenergy conditions for surface charge. Atthat time ESO placed a contract to thinand optimize four LORAL devices of 2Kformat, 15-flm pixel size, 2-side buttabledesign, and first results are expecteduntil the end of 1993.

9

Figure 2: Sketch o{ the GGO design {oreseen tor the VLT test camera: a 20482, 24-pm scienti{icGGO, surrounded by tour tracker GGOs, o{ two different sizes.

Currently, a follow-up contract forthinning and optimization of six 20482

,

3-side buttable LORAL South CCOs(described in the previous paragraph) isin preparation. It foresees the delivery ofthe final thinned CCOs, requiring UVflooding, in June 1994. A packaging

10

construction with similar mechanical in­terface as for the Thomson CCOs ofidentical format (described above) isunder study in order to simplify potentialexchanges of the two.

As a consequence, these devices rep­resent an alternative to the Thomson

CCOs and could be used in all applica­tions for which these are planned.

6. Concluding Remarks

The more recent main CCO procure­ment activities for the VLT have beendescribed here in a summarized form.The assessment of the probability of agiven development to be completedsuccessfully has to be updated on aweekly basis depending on the techni­cal results obtained by the manufactur­ers in the various phases of their pro­cessing. Another source of worry is thefact that the CCO field has - especiallyin 1993 - undergone dramatic changesconcerning the future of major suppliers,with recurring announcements of clo­sures of manufacturing lines and ofchange of property.

The limitation on ESO manpower andbudget considerations necessarily limitthe number of parallel developments wecan carry out, but the floating situationforces us, as weil as any other groupworking in this field, to systematicallyexplore alternative routes of procure­ment in industry and in researchlaboratories. These might become thesingle alternative solution of the future.

In many observing modes of the VLT,the photons collected by the 8-mmirrors end up on the few square cm ofthe CCO detectors and the success orfailure of the best scientific programmeof European astronomy can depend onthe final performance of these devices.While sometimes one feels the weight ofthis responsibility, this is what ultimatelymakes the work in this field so excitingand any result towards better detectorsso much rewarding.

SCIENCE WITH THE VLT

The Limits of Faint-Object PolarimetryR. FOSBURy1 (ST-ECF), A. CIMATTI (ESO/Florence, Italy)

s. 01 SEREGO ALiGHIERI (Arcetri, Italy)

Introduction

A common problem in observationalastrophysics is the investigation of com­plex geometrical structures which arebelow the resolution capabilities of tele­scopes. In some cases, small-scalestructures can be inferred from the glo­bal morphology, e.g., the beautiful "ioni­zation cones" seen in some of the near­by Seyfert galaxies (Figure 1), but a ge­ometry-sensitive tool is needed in orderto make real progress with the inferenceof the fundamental physical processes.

The study of rapid time variability hasbeen valuable for the determination ofphysical scale sizes and, in some cases,the discovery of bulk relativistic effectsas an explanation of apparent superlum­inal motion. It is polarimetry, however,which is capable of giving us the mostdetailed information about "directionali­ty". This is, of course, a well-establishedtechnique in astronomy with many ap­plications in many wavebands. Polari­metric studies cover a wide range ofastrophysical subjects. In particular, itis important for solar system objects, inmany fields of stellar astrophysics (star­forming regions, young stars, binarysystems, variable stars, pulsars, etc.)and in all extragalactic sources, fromnormal galaxies (magnetic fjelds, ISM) toactive galaxies and asos (synchrotronemission, ISM, scattering, geometry). Itis not our intention to review here eitherthe applications or the physical pro­cesses and observing techniques.Rather it is to concentrate on a particu­lar aspect of the subject wh ich hasyielded a rich harvest of new results onfaint sources with the current generationof 4-m-class telescopes and promiseseven more from the yet-Iarger photoncollectors which are just starting to be­come available. This is the study of thesurroundings of active galactic nuclei(AGN) which show many indications of apredominantly axial symmetry deter­mined by the properties of the funda­mental source of luminosity.

Following the discovery of the "align­ment effect" in high-redshift radio galax­ies (HzRG) by McCarthy et al. (1987) and

1 Affiliated lo lhe ASlrophysics Division, Space Sci­ence Department, European Space Agency.

by Chambers, Miley & van Breugel(1987), there has been considerable in­terest in trying to disentangle thosecomponents in the galaxies which cantell the story of their stellar evolutionaryhistory from those which are the resultof the presence of a powerful AGN.These objects show a roundish, redcomponent and an irregular blue struc­ture which is aligned - but not necessar­ily coincident - with the extended dou­ble radio source (Rigler et al. 1992, Oun­lop & Peacock 1993). Attempts to ex­plain the elongated blue componenthave centred on two mechanisms. Oneproposes that the particle jets whichdrive the extended radio source some­how trigger the formation of stars asthey traverse the galaxy ISM (Rees1989, Oe Young 1989). This young stel­lar population shines brightly in the UVand, rather like the track of a particle in abubble-chamber, traces the radio axisbefore dynamical effects in the galaxysmear the structure. The second derivesfrom the hypothesis that powerful radiogalaxies and radio quasars are one andthe same type of object and differ inappearance only by the inclination of theradio axis with respect to our line-of­sight. This unification scheme clearlyimplies the presence of a quasar nu­cleus in the HzRG which, as proposedby Tadhunter et al. (1988), will have pro­found effects on the ISM and will beimpossible to hide - especially in theultraviolet where the galaxy host may berelatively faint.

Optical observations of the HzRG withz ~ 1 sampie the rest-frame UV and so itis not surprising that they show signifi­cant morphological differences fromtheir (extremely rare) low redshift coun­terparts which are observed in the opti­cal. One important question we have toanswer, whatever the correct explana­tion of the alignment phenomenon, iswhether these differences are entirelydue to the different wavebands of theobservations or whether we see evolu­tionary effects in addition. Our polariza­tion observations have been directedtowards testing the hypothesis that theblue, aligned structures result from thescattering of the nuclear quasar com­bined with locally generated linefluorescence excited by the EUV con-

tinuum. Clearly, the scattering will pro­duce a linear polarization signature witha precisely defined geometry having theelectric vector perpendicular to the di­rection of the illuminating source in thenucleus. This is a strong hypothesissince, with the appropriate observa­tions, it is readily refutable.

Techniques

The determination of polarization de­mands the measurement of intensityratios. For faint extragalactic sources,the fluxes from which the ratios areformed are measured in the presence ofa strong, and generally polarized, skybackground. Even small variations inthis background would make sequentialmeasurements of different polarizationdirections prone to severe systematicerrors. The techniques in common use,therefore, make flux measurements inorthogonal polarization directions simul­taneously The method that we use withEFOSC1 (see The Messenger, Sep­tember 1989, No. 57) for both imagingand spectro-polarimetry employs aWollaston prism in the parallel beamand an aperture mask in the focal planeof the telescope. The mask ensures thatthe sky from one polarization is notsuperimposed on the object in the other(Figure 2).

We have used this method to mea­sure polarizations in radio galaxies withredshifts as high as 2.63 and fainterthanan R magnitude of 22. Our experiencehas been that, for these faint objects,the accuracy of the measurement is rel­atively free from systematic effectswhile the precision is entirely limited bycounting statistics with CCO detectors.Instrumental polarization - which is<1 % for imaging and <5 % for spec­tropolarimetry - is straightforward tomeasure and correct for by looking atfield stars and polarimetric standards.The critical part of the analysis is, fairlyobviously, the extraction of the objectflux - including faint extensions - fromthe background. Optimum methods fordoing this, using high s/n sums of allthe individual observations to definea weighting scheme, are being de­veloped.

11

Figure 1 a: An example of ionization cones in the nearby Seyfert galaxy NGC5252 (Courtesy ofZ. Tsvetanov & C. Tadhunter). The two images ­with the same scale and orientation - show at the left line-free continuum (starlight) and at the right [OIlI}/5007 line emission (excited by theAGN).

Blazarbeam

lonization cone

Figure 1 b: A cartoon of the origin of theionization cone phenomenon by shadowingclose to the AGN. In addition is shown theblazar beam which is thought to be producedby Doppler boosting in regions associatedwith the formation of the radio jet in radiogalaxies. The radio-quiet Seyferts show noevidence of a blazar component.

implieations for our understanding ofmassive galaxy formation.

In reeognition of the fact that the VLTwill give very important gains for polari­zation measurements, most of the

Image

planned instruments will have polari­metrie eapabilities whieh are briefly re­viewed here.

FORS, an imager/speetrograph de­signed to work at the Cassegrain foeus

Camera

Wollaston prism

Given our experienee with the 3.6-mteleseope, it is straightforward to ex­trapolate to the eapability of an 8-m VLTelement. The new, large teleseopes aregoing to give enormous gains in thistype of measurement and will allow de­tailed polarization mapping and high­resolution speetropolarimetry wherenow we struggle to do broad-band"aperture" polarimetry and eoarse-reso­lution speetral measurements. The abili­ty to reaeh galaxies at redshifts greaterthan one and to separate stellar andnuelear eomponents will have profound

12

Collimator

Focal-plane grid

Figure 2: A schematic view of an imaging polarimeter using a Wollaston prism to split thepolarized beams and a focal-plane mask to avoid overlapping images at the detector. At ESO,this facility is available with EFOSC and can be converted for spectropolarimetry by adding agrism in the parallel beam. An achromatic half-wave plate has been obtained and will shortlybe added to the instrument so that the plane of polarization can be rota ted with respect to themask. This is especially important for spectropolarimetry.

R 0

Figure 3: A three-dimensional plot of the analytie distribution funetion (a Riee distribution) forthe linear polarization measured in the presenee of poisson noise. The x-axis shows themeasured polarization (normalized to the observational a), while the y (depth)-axis showsthe similarly normalized true (input) polarization. The distribution beeomes highly skewed asp/a ---? 0 and so the resulting measurement bias must be removed.

between 330 and 1,100 nm with spec­troscopic resolution up to 2000, willhave both imaging- and spectro­polarimetry modes. These are providedby rotatable retarders and a Wollastonprism to be used in combination withfilters or grisms and focal plane masksor slitlets. lt is anticipated that the degreeof linear polarization will be measuredwith an accuracy of 1% in one hour downto U, S, V and R magnitudes of 22-23 inimaging and down to V= 17.3 in spectros­copy with 2.5A resolution.

ISAAC, the IR imager/spectrographfor the Nasmyth focus will work be­tween 1 and 51lm with spectroscopicresolutions in the range 300-10,000. ltwill do imaging polarimetry using a fixedanalyser in one of the filter wheels, to beused in combination with filters and withrotation of the whole instrument.

Similarly, imaging polarimetry will bepossible with CONICA, the high spatialresolution, near-IR (1-5Ilm) camera.This is designed to work at the coudefocus in combination with adaptive op­tics but the effects of the coude opticaltrain on polarization measurementshave yet to be carefully assessed.

UVES is an echelle spectrograph forthe Nasmyth with a spectroscopic reso­lution of 40,000. The possibility of doingspectropolarimetry with a polarizationanalyser in the pre-slit optical train hasbeen investigated, but is not in the pres­ent plan because of possible difficultieswith the polarization induced by M3, theimage slicer, the image derotator andthe spectrograph. Nevertheless theseproblems are not insoluble and polari­metry with UVES would be useful, e.g.,to study the line polarization structure inAGN.

The present design of the 10-20 IlmCassegrain imager/spectrograph anti­cipates that both imaging- and spectro­polarimetry will be possible with a rotat­able retarder and fixed analyser.

Simulation and Error Estimates

The state of polarized light is de­scribed by the four Stokes parameters,I, Q, U and V. These can be normalizedto unit intensity for the light source and itis then the second two components ofthe vector, q and u from which the stateof linear polarization is derived. In apractical polarimeter, q and u are rep­resented by appropriate intensity ratiosin orthogonal polarizations. Whenpoisson noise from the object and thesky is the only source of error, the dis­tribution functions of q and u arestraightforward to calculate and onlybecome non-normal at very low signal/noise ratios (Clarke et al. 1983). Thequantities of direct astrophysical inter­est, the degree of polarization p and

Probability

0.6

0.4

p/cr

the orientation of the electric vector{), are derived from q and u as theirquadratic sum and the arctangent oftheir ratio respectively. The distributionfunctions of p and {) are no longer nor­mal and that of p becomes skewed asp ~ 0 (Figure 3). These distributionfunctions have to be calculated, eitheranalytically or by Monte-Carlo simul­tation, before proper confidence limitscan be attached to measurements(Simmons & Stewart 1985, Clarke &Stewart 1986). Secause of its skeweddistribution, measurements of p close tozero are biased and this has to be re­moved using the calculated distributionfunction (Wardie & Kronberg 1974).

While the analytic functions can beused to reduce observations, we havefound it convenient to build a stochasticmodel of the polarimeter which can bereadily adjusted to match a particularobservational setup and set of measure­ment angles. In addition to calculatingthe distribution functions for the quan­tities of interest, the simulation can beused to optimize the use of a givenamount of observing time amongst asequence of exposures at differentorientations of the polarizing prism. Ourversion is implemented in the lnteractiveOata Language (IOL) and runs on a Sunworkstation. A typical run of 30,000trials for a set of four angles takes just afew minutes on aSpare 10. The sampieoutput shown in Figure 4 represents aset of imaging observations of thez=2.63 galaxy MRC2025-218 (Cimatti

4

Pdcr

et al. 1993b). In this case, q and u arethe amplitudes of the sine and eosineterms in a sinusoidal fit to a set of inten­sity ratios at different orientation anglesof the instrument. The bias in the mea­surement of p is obtained by comparingthe value input to the simulation withthat derived from fitting the peak of thep-distribution. These observations useda total observing time of 270 min on the2.2-m and 3.6-m telescopes and areclose to the limit of what can beachieved with these instruments. Thesame precision could be reached in lessthan an hour with the same type ofinstrumentation on an 8-m telescope.

Scientific Highlights

The first detection of polarization inHzRG with z > 1 was in 3C 386 and3C277.2 (di Serego Alighieri et al. 1989)and this was followed by a polarizationmap of 3C368 made by the Ourhamgroup (Scarrott, Rolph & Tadhunter1990). There are now measurements ofsome forty objects with z>0.1 (Cimattiet al. 1993a) and a remarkably well­defined trend is emerging. The degreeof linear polarization is strongly corre­lated with the rest wavelength of theobserved radiation (Figure 5). For a giv­en filter, this manifests itself as a corre­lation with redshift but it appears thatthe wavelength dominates any evolutio­nary effects (Cimatti et al. 1993a). Forthose objects observed at a restwavelength below 4000A, the polariza-

13

Sunusoidal fits for q & uo,20 rTTTT"rrr""TT"TT"1rTTTT1rrTTT"rrr-rrrnm-rrrrrTrT"TT1

0,200.150,100.05O'----<_'--'--'-..L--'---'--'-..L--'--'--"---'---J....-l....................~0,00

600Polarization distribution

100

200

300

400

500

30:)2DOphi

100o

0,10

-0,10

...-..L'c.. -0,00-.....r(I)

2000Theta distribution

I

Stokes parameters q & u0,20

1500 0,10 f-----+-----+-----+-----l

1000

5DO

III

~ -0,00

~

-0,10 I------t-~-_+---_+--_____i

0,200.10-0.10- 0 ,20 U-1...u....u...U-.l...u....u...U-.l...u..~.L..Wu...L..J....L..L..Wu...L..J....L..L..Wu..w

-0.2020015050 100 -0,00stokes lJ

Figure 4: A representation of our stoehastie model of imaging polarimetry. This shows the measured data for the high redshift radio galaxyMRC2025-218 (z=2.63) from the ESO 2.2 and 3.6-m teleseopes. In cloekwise order, the four frames show: (1) The measured data points withtheir 1s error bars (red stars) and the fitted sinusoid (blue dashes). The yellow eurves represent every thousandth fit to 30,000 simulated datasets with poisson noise added to sky and objeet counts. (2) The polarization distribution resulting from the simulations. The gaussian (green) andparaboloidal (red - fitted to the peak only) fits are used for finding the most probable polarization. This measurement eorresponds to a pis of 3. 8and so the distribution funetion differs only slightiy from anormal eurve. (3) The distribution funetion for the position angle of the E-veetor. (4) Thedistribution of simulated points in the q, u-plane. The eireles represent 67 %, 90 % and 95 % eonfidenee limits.

tion is generally higher - ranging up to20 % - than the objects observed atlonger wavelengths and has an E-vec­tor wh ich is, in all measured cases, per­pendicular to the radio axis within themeasurement error.

Spectrapolarimetry (di Serego Ali­ghieri, Cimatti & Fosbury 1993 and inpreparation) shows this polarizationdrap longward of 4000A very clearly intwo individual objects. This is inter­preted as the increasing dominance ofunpolarized starlight above the H&K­break fram an old stellar population (Fig­ure 6).

Attempts to model the spectral ener­gy distributions and polarizations ofthese HzRG using a combination ofstarlight and scattered quasar light arehampered by the paucity of spec­trapolarimetric - or line-free imagingpolarimetrie - data. They do, however,indicate that it is possible to reproducethese two types of measurement simul­taneously using an old stellar populationand scattering by dust. Electron scatter­ing cannot, however, be ruled out andremains a possibility especially close tothe nucleus and, possibly, for sources inrich clusters.

Taken with other tests of the radio­loud unification scheme, the polarimetrypravides very strang evidence that theHzRG indeed harbour obscured quasarnuclei. Many details, however, remain tobe investigated. For example, it is notknown how much the blazar beam ­thought to be present in all radio-Ioudquasars - contributes to the scatteredradiation. This will have a bearing on therelative strength of any scattered broad­line radiation. There is also evidencethat the non-stellar continuum radiationfram AGN may be as extended or evenmore extended than the BLR (Binette,

14

60005000

Dunlop J.S., Peacock JA, 1993, MNRAS, inpress.

McCarthy P.J., van Breugel w., Spinrad H. &Djorgowski S., 1987. Ap J, 321, L29.

Rees, M., 1989. MNRAS, 239, 1p.Rigler, MA, Lilly, S.J., Stockton, A., Ham­

mer, F. & Le FEMe, 0., 1992, Ap J, 385, 61.

Scarrott, S.M., Rolph, CD. & Tadhunter,C.N., 1990. MNRAS, 24, 5p.

Simmons, J.F.L. & Stewart, B.G., 1985, A&A,142,100.

Tadhunter, C.N., Fosbury, RAE., di SeregoAlighieri, S., 1988. In: "BL Lac Objects",Maraschi, L., Maccacaro, T & Ulrich, M-H.,eds. Springer-Verlag, Berlin, p. 79.

Wardie, J.F.C. & Kronberg, P.P., 1974. Ap J,194,249.

H&K• break

3000

+

2000o

10

20

P (%)

4000Arest (A)

Figure 5: Linear polarization measurements for radio galaxies with z>O. 1 collected by Cimattiet al. (1993a). The arrows represent upper limits and the different symbols are from differentobservers. The fractional polarization is plotted against the wavelength of the filter passband inthe rest-frame of the galaxy. All the delecled polarizations 10 the left of the H& K break haveE-vectors perpendicular to the radio axis.

Cimatti, A., di Serego Alighieri, S., Field, G.M.,G.M. & Fosbury, R.A.E., 1993b, ApJ, inpress.

Cimatti, A., di Serego Alighieri, S., Fosbury,RAE., Salvati, M., & Taylor, D. 1993a,MNRAS, 264, 421.

Clarke, D. & Stewart, B.G., 1986. Vistas inAstron. 29, 27.

Clarke, D., Stewart, B.G., Schwarz, H. E. &Brooks, A., 1983. A&A, 126, 260.

De Young, D.S. 1989. ApJ, 342, L59.di Serego Aligllieri, S., Fosbury, R.A.E.,

Quinn, P.J. & Tadhunter C.N., 1989. Na­ture, 341, 307.

di Serego Alighieri, S., Cimatti, A., Fosbury,R.A.E., 1993, in Active Galactic Nucleiacross the Electromagnetic Speclrum,Courvoisier et al. eds., in press.

ReferencesAntonucci, R., 1993. In: lAU Symposium

#159. "Active galactic nuclei across theelectromagnetic spectrum", Geneva, 1993.

Binette, L., Fosbury, RAE. & Parker, D.,1993. PASP, 105, 1150.

Chambers, K.C., Miley, G.K., & van Breugel,W. 1987, Nature, 329, 604.

Conclusions

Both imaging and spectropolarimetryare now playing an important role in theunderstanding of the AGN phenome­non. We have discussed here only thepolarization produced by scattering. In­trinsically polarized emission mecha­nisms like synchrotron radiation arealso, of course, the subject of intensivestudy in these objects. The nearby Sey­fert galaxies can now be studied in greatdetail using polarimetrie techniques,and we fully expect to be able to emu­late such investigations at cosmologi­cally interesting distances when wehave access to the bigger telescopes.The extension of the measurements intothe infrared will also be interesting,especially for resolving the electron vs.dust scattering question.

Finally, we stress that the use of spec­tropolarimetry to identify and removethe AGN contribution to the luminosityof very distant radio galaxies can allowdeductions to be made about theirstellar evolutionary histories with muchgreater confidence than pure spectros­copy. The epoch of galaxy formation isone of the outstanding questions in cos­mology today.

Fosbury & Parker 1993, Antonucci 1993)which will also have an effect on theratio of line to continuum radiation inpolarized light.

>'+-,0)o

.....J

Photometrie bands/-----------

/ ------/

//

//

//

//

/

v

Figure 6: A cartoon of the speclral energy distribution of a HzRG adapted from Rigler et al. (1992). This shows the two spectral componentswhich will alternalively dominate the measured flux above and below Ihe H&K break in the resIframe of the galaxy. We identify the bluecomponent with the alignment effecl which results from fluorescence and scattering processes powered by the AGN.

15

REPORTS FROM OBSERVERS

CCD Astrometry. No, Really - It is Interesting!c. G. TlNNEY, ESO

Introduction

In recent years, the field of astrometry- usually considered a stuffy backwaterby most astronomers - has been re­vitalized by the introduction of CCOsinto general astronomical use. Not onlyhave these devices made photographicplates outdated for most astrometricpurposes, but they have significantlyadvanced the precision with which as­trometry can be done. In the processthey are turning astrometry from a fielddominated by large, long-term mea­surement programmes and endless re­ductions of celestial co-ordinates, into avital and fundamental contributor to cur­rent research programmes. In this ar­ticle, I'd Iike to show what CCOs can(and can't) be used for, why they are somuch better than photographic plates,how easy it is to do astrometry withthem, and to look at where progress inthis field can be expected to go.

What CCO Astrometry Can't 00

Of course, no device is perfect, andthere are some astrometric applicationsfor which CCOs have not proved suc­cessful. Perhaps the most serious un­solved problem is that of dynamicrange. Whereas photographic platescan be successfully used for astrometrywhen the cores of images are saturated,no technique has yet been devisedwhich allows saturated CCO images tobe centroided with the same precisionas unsaturated images. This is a majorproblem for the astrometry of distantand bright objects, like Galactic giants,supergiants and AGB stars - these in­clude, of course, the distance-indicatorobjects everyone would like to obtainparallaxes for; Cepheids and RR Lyraestars.

The difficulty is that these stars areintrinsically very bright, and rather rare.So, within a given CCO field-of-view thenumber density of stars suitable for useas reference objects is very small - toobtain sufficient counts on the intrinsi­cally fainter background stars requiressaturating the programme object.Photographic programmes deal withthis by the deposition of uniform Ni­chrome attenuation spots onto filtersmounted against the plates, allowingselective dimming of the programme

16

star. However, astrometric results withthe precisions attained by CCO pro­grammes have yet to be obtained withany magnitude compensation systemand a CCO. This means that while CCOastrometric programmes can obtainparallaxes to more distant stars thanphotographic programmes, they canonly do so for relatively faint 01 ;z: 15)magnitudes.

The second difficulty with CCOs is thelimited size in which they are currentlyavailable. Photographic plates can bepurchased (at least for the immediatefuture) in sizes up to "" 400 mm on aside. The largest CCOs currently avail­able are more like 50 mm in size. Thismeans that CCOs cannot be used forapplications requiring wide-angle (i.e. ;z:20-30') astrometry. However, this maynot be as serious a problem as it seems.Studies of the astrometric effects of theatmosphere have shown that the residu­als produced in astrometric solutionsincrease with the FOV used and de­crease with exposure time (Han 1989,Monet & Monet 1989). This means thatfor useful exposure times (- 1000s),solutions for reference frames in fieldsof "" 20' never get much better than ""10 mas1

- and this uncertainty scalesroughly as both the one third power offield size and inversely with the squareroot of the exposure time. This meansthat for large fields of view (- 1°), thelimiting precision is set by the atmo­sphere, not the detector, and the use ofCCOs may produce no gain. It also im­plies that taking short exposures in or­der to avoid the saturation problemsdescribed above significantly degradesastrometric performance.

What CCO Astrometry Can 00

So, those are the minuses - you can'tmeasure very bright stars, and you can'tmeasure very large angles. However,those are exactly the classes of objectfor wh ich HIPPARCOS will be producingsuperior astrometric data in the next fewyears in any case. It is in measuring faintobjects - objects which HIPPARCOScan't reach - that ground-based CCOastrometry really finds its niche.

1 "mas" is used as an abbreviation for milliarc­second lhroughout.

Perhaps the biggest advantage whichCCOs provide for astrometry is thatsince CCO data are inherently digital,they can be easily evaluated as obser­vations are being carried out. In particu­lar, this means that the observer canexamine test images, and place the pro­gramme object back in exactly the samelocation on the telescope's focal planeas the last epoch's observations. Theimmediate result of this is to allow CCOastrometry to be almost purely differ­ential - except for applications requiringthe highest of precision, the telescope'sfield distortion becomes irrelevant.

Second, CCOs have much higherquantum efficiencies than photographicplates - allowing the observation ofobjects - 3 magnitudes fainter for agiven telescope and observing condi­tions. In particular, they are more sensi­tive in the red. This latter point is espe­cially important because the astrometriceffects of the atmosphere become lesssevere when observations are made atred wavelengths.

And lastly, because the matrix of pix­els in modern CCOs are so regular,and charge-transfer efficiencies are sogood, the precision of centroiding be­comes almost photon-counting limited- the more photons you collect the bet­ter your position comes. This allows im­ages to be centroided to hundredths ofan image size. Photographic plates, onthe other hand, have an irregular matrixof grains, and they also must be di­gitized with a measuring machine, withall the mechanical uncertainties thatthose machines introduce. It should benoted, though, that centroiding to thisprecision requires that all the objectshave the same point-spread-function,that is they must be unresolved. (Thishas important implications for the as­trometry of the very distant objects. Ifextragalactic reference objects are re­quired, they must be asos - galaxieswill not do.)

Taken together, these advantagesallow astronomers to acquire astrometryat the several mas-Ievel in a verystraightforward manner, using the com­mon-user CCO instruments now avail­able at most telescopes. Moreover, theyallow more dedicated astrometric pro­grammes to push precisions below themas-Ievel. The pioneers in this field have

been the US Naval Observatory's Flag­staff station, which has been carryingout a CCO parallax programme since1983 (see Monet et al. 1992). This pro­gramme has been so phenomenallysuccessful, that it has led to the termi­nation of the observatory's long-runningphotographic programme. Its successhas also led to the initiation of smallerastrometric programmes at other obser­vatories - most notably, Mt. Stromlo(Ianna 1992), Cerro Tololo (Ruiz et al.1991) and Palomar (Tinney 1993a).

These programmes, however, havebeen significantly different from mostprevious astrometric programmes. Tosome extent, astrometric programmeshave traditionally been carried out ondedicated, small aperture telescopesand have targetted large numbers ofstars. They have tended to be run as a"service" to the astronomical communi­ty, rather than with a specific and im­mediate scientific goal in mind. Theease of doing astrometry with CCOs,however, has changed that. The smallerprogrammes listed above have all beenscientifically motivated, and targeted atparticular classes of objects of interestto the astronomers concerned. In short,they are no different from any other typeof astronomical project.

"""'~\"'''>n'''''''=~'m ' .~'ilWr."fu::&l.~.iiIl>;,~J.:iiFigure 1: A typical GGO frame of the recently discovered VLM star TVLM513-46546 (north isup, west to the left. The object is marked with abox).

"Do-It-Yourself" Parallaxes

The Palomar Parallax programme wasmotivated by the need for more paraI­laxes for the very faintest of main se­quence stars. A p'lotometric survey forthese stars (Tinney 1993b, Tinney, Reid& Mould 1993), had indicated a need formore Very Low Mass (VLM, M $ 0.2Mdstars with measured distances, in orderto define the colour-magnitude relationsessential for photometric selection ofthese stars. The USNO's results encour­aged us to try and obtain these parallax­es for ourselves, rather than rely on theirheavily overburdened programme.

Observations were carried out at fiveepochs per year (roughly evenly spacedthroughout the year so as to providegood sampling of our VLM surveyfields), with the Palomar 60" (1.5-m) te­lescope. The CCO used was a Tektronix1024 x 1024 thick, front-side illuminateddevice. When mounted at the Casse­grain focus of the 60" the CCO's 24f.lmpixels gave a scale of 0.372"/pix. Thefield-of-view then was = 6' - this wasfound to be sufficiently large to providea good background reference frame ofstars for our programme objects, wh ichwere situated at b - 40° - 60°. Allobservations were carried out through aGunn i filter (I'eff = 790nm, tJ.f... = 100nm).The choice of this filter was motivatedby several factors; first, the target starswere all extremely red, making observa-

tions at as long a wavelength as possi­ble desirable; second, the effects of at­mospheric differential colour refractionare minimized by observing in the red;and third, as the CCO used was front­side illuminated, observing at a redwavelength reduces the sub-pixeleffects of observing through the CCOsfrontside gate structure.

Multiple images (3-4) of each pro­gramme object were obtained at highparallax factors several times a year.Some effort was made to place objectsat roughly the same location on the CCOat each epoch. All the data were flat­tened with dome flats. The stellar im­ages were centroided using OAO­PHOT - we found that each observationcould be centroided to about 1/20Othof an image size. That is, for a starof 1=16.5, a single 300s exposure in 1':0seeing gives a position good to = 5 mas.(Observations were not carried out inseeing worse than 2':5 - It was found tobe not worth the time spent reducing thedata). All our observations were mappedonto a common coordinate system us­ing a reference frame of backgroundstars - since our programme objects areintrinsically very faint, an average back­ground star of similar magnitude is morethan 100 times further away, makingcorrections from relative to absoluteparallax very smalI. A sampie CCO frame

for one of our programme objects(TVLM513-46546) is shown in Figure 1.Figure 2 shows its preliminary astromet­ric solution as derived in Tinney (1993a).Over the 2 years for which data havebeen reduced to date we typically ob­tain parallaxes with 2-3mas uncertain­ties. Over the total 3 years which ourprogramme will run (observations willterminate in November 1993) we expectto obtain parallaxes with uncertainties of1-2 mas. For the one object we havemeasured in common with the USNO(VB10), agreement was found within ourestimated 1-0 uncertainties (Monet et al.1992).

The greatest problem to surmount incarrying out a parallax programme forthese stars, is dealing with the effects ofdifferential colour refraction (OCR) ­put simply, the reference stars have ashorter effective wavelength through theGunn i filter than the much redder pro­gramme stars. This results in the pro­gramme stars suffering less atmospher­ic refraction than the reference stars.However, so long as observations aremade reasonably close to the meridian,this effect can be substantiallycorrected. We do this by observing eachobject as it rises and sets on a singlenight. The motion introduced by OCRcan then be measured and calibratedout on subsequent nights. We found

17

LEGEND00n • 07AUG91 211-PR920

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0 ....... . ,- ..... .... x 30JAN92E .............ö ;L<J

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1~ ---(fl

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Sl 0 JI on600 650 700 750 800 850 I

1SO 200 2SO )0:>

JUUAN DATE - 2447891.5 (0 Jon '990). t::.a (mos)

Figure 2: The pre/iminary astrometrie solution for this objeet (Tinney 1993a).

Figure 3: (a) The M,//-K diagram as known eirea 1985. (b) The eurrent MI//-K diagram, ine/udingparallaxes from the Pa/omar (stars, Tinney 1993a), USNO (squares and eire/es, Monet et a/.1992) and Mt. Strom/o (triang/es, /anna 1992) programmes.

MEo1 = 11

MEo1 = 13

MEo1 =12

54

I-K

32

(()

N

Higher precisions can be achieved byobserving reference frames over smallerfields of view, so long as a rich enoughfield of unresolved objects is available totransfer all the data onto a common co­ordinate system. Narrow-band filters,longer integration times and larger tele­scopes should be used to minimize theatmosphere's effects whenever possi­ble. Sites with superior seeing shouldobviously also be preferred. By takingadvantage of all these, it should bepossible to push the astrometry of faintobjects below the 1-mas barrier.

o

(b)

MEo1 =13

54

I-K

32

(()

[I] ClCl

N _ fIlnrn-·_·_·Cl·_·-ID"·_·_·_·_·_·_··.. _· M

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[I] Cl

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_.Jll~._._._._._._._._._._._. MEol

=11~rn

sions? Currently, the barrier preventingsub-mas astrometry is the atmosphere- both due to differential c%ur refrac­tion, and due to differential seeingeffects. The obvious solution is to carryout astrometry from space with a CCOcamera, something the corrected HSTmay be able to do. But in the nearerterm, what can be done from theground? It turns out that there are anumber of regions in the "observingphase space" which have yet to be fullyexplored, and which may produce someexciting new results.

(a)

that our use of a Gunn i filter gave us asignificant reduction (a factor of about 4)in the amount of OCR observed, com­pared with that seen at the USNO,where a much wider filter (/\,eff = 690 nm,i",')... = 300 nm) is in use. This means thatwhile we need to take longer exposures,we have considerably more flexibility inscheduling, since we can observe = 4times further from the meridian for agiven OCR effect. For a non-dedicatedfacility this flexibility is important. In anycase, longer exposures allow differentialseeing effects over the field of view tobe averaged out and therefore increasesastrometric precision.

Figure 3 shows how this small pro­gramme has been able to make a signifi­cant contribution to the specific prob­lem it was designed to address. The firstpanel shows the colour-magnitude dia­gram as it existed when our VLM surveywas begun, the second shows it as ofearlier this year. Almost half of the VLMstars (M so1 > 13) which now have paraI­laxes come from the Palomar pro­gramme. It is also worth noting that bycarrying out our own parallax observa­tions, this improvement could be ob­tained quite quickly - the total time be­tween the identification of TVLM513­46546 as a VLM candidate and the mea­surement of its absolute magnitude (it isthe second faintest VLM star known)was only 18 months.

Pushing Back the Envelope

If "common-user" astrometric pro­grammes can obtain results at the sev­eral mas level over only a few years,what are the prospects for specializedprogrammes to achieve higher preci-

18

Figure 1: ESO 50-cm telescope with the TV guiding system ofFLASH. The total weight of the guiding system is only about 35 kg. Itcontains the fiber-fed interface, comparison lamps and a conven­tional SIT low-Iight-Ievel camera.

Figure 2: Our spectrograph with GGO and GGO electronics, in thesmall cabin at the concrete base of the telescope, the smallest couderoom in the world. In the background some counterweights of thetelescope balancing system can be seen.

plifies the merging of the reduced differ­ent echelle orders. One also eliminatesflexure problems while housing the in­strument in a temperature and humiditycontrolled room. Ouring observing at theESO 50-cm telescope the spectrographwas placed in the small cabin at theconcrete base of the telescope behindthe astronomers office with only twoconnections to the outside world, oneincoming fiber and one outgoing coaxialcable.

With an efficient detector, stars downto a magnitude of 7 are in the reach ofthe ESO 50-cm telescope. Using an EEVCCO with 1252 x 770 pixel of 22 fl, weget 2700 Ä in one exposure. At standardsetup we selected the wavelength rangefrom 4050 to 6780 Ä. This setting allowsobservations of 57 echelle orders simul­taneously, with a generous overlap be­tween the orders. With a 100 fl fiber,wh ich corresponds to 2':75 at the ESO50-cm telescope, the spectral resolutionis about 20,000. Ouring observation, upto 100 CCO frames (including ThAr- andflatfield-spectra) can be stored on thehard disk of the CCO control computer.

20

These frames are transferred to magne­tic tapes each morning and later copiedto OAT-tapes by ESO.

Luminous Blue Variables

Apart from supernovae at outburstLBVs are the most luminous stars in theUniverse (M "" -9 to -11). For morerecent reviews see Wolf (1992) andStahl (1993). The LBVs have recentlybeen recognized as keys in connectionwith the evolution of massive stars. Atquiescence they define an inclined in­stability strip of OB supergiants (Wolf,1989) close to the Eddington limit. Theyare characterized by photometrie varia­tions of 1 to 2.5 mag in timescales ofyears and longer. At maximum bright­ness they are surrounded by cool("" 8000 K), dense (N "" 1011 cm-3) slow­Iy expanding (v "" 100 km S-1) envelopesof typically equivalent spectral type A. Inaddition to the large outbursts, photo­metrie microvariations of 0.1 to 0.2 magon timescales of 1 to 2 months or morehave been found in all those cases ob-

served in more detail (van Genderen,1989).

Ouring the past decade our group hasobserved spectra of the established andnewly discovered LBVs of the Galaxyand of the Magellanic Clouds more orless regularly each year at La Silla withCASPEC. The exhibited long-termspectral variations shown by the LBVshave been of vital importance for abetter understanding of the outburstphenomenon. They have contributedquite considerably to derive the generalpicture sketched above. On the otherhand, with snap shot observations, typi­cally separated by one year, the detailedhydrodynamic processes cannot bestudied.

The Campaign

For a better understanding of the at­mospheric motions, systematic spec­troscopic monitoring over a time spanof months with good resolution inwavelength and time is badly needed.We therefore applied for two contiguousobserving runs of two months each at

But what can you do with that sort ofastrometry? The prospects are enor­mous - to name just a few: parallaxes ofmore distant and/or fainter classes ofobjects like very low-mass white dwarfs,optical counterparts of neutron stars,and brown dwarf candidates; orbits forclose (2-10") binaries; proper motionsof globular clusters, and proper motionswithin globular clusters; and proper mo­tions for the Galaxy's satellite galaxies.

There are also prospects for CCOs tobe extended towards the observation ofbright stars - those objects too faint forHIPPARCOS and too bright for currentCCO techniques, or those objects toodistant for HIPPARCOS. The use of anti­blooming techniques, and the develop­ment of CCOs with larger full-wellcapacities, may allow precise astrome­try to be done with the brightest stars.An alternative technique, being exploredat the USNO, is to carry out observa-

tions with a CCO mosaic, bonded onto asingle silicon substrate, in which one ofthe CCOs is configured as a frametransfer CCO, allowing very short (andunsaturated) exposures of a target star,while the surrounding CCOs acquiredeep images of the surrounding starsfor use as reference objects.

Conclusion

I've tried to show, in the sectionsabove, some of the interesting resultscurrently being obtained with CCO as­trometry, some of the exciting pros­pects for its future, and how straightfor­ward it is to actually do it. Several pro­grammes at La Silla currently use CCOsfor astrometric purposes, both forstudies of the solar system and nearbystars, and future programmes areplanned to expand on their use for theselocal studies. Within the next year, I

hope to carry out test observations withthe ND, to explore its use for high pre­cision astrometry below the 1-masbarrier in studies of the Galaxy'ssatellites. It is my hope that the activityin this field will encourage more mem­bers of the general community to inves­tigate this "rediscovered" astronomicaltechnique - one which shows such as­tounding promise for the future.

ReferencesHan, 1., 1989, AJ, 97, 607.lanna, P., 1992, lAU Symposium 156, ed:

Mueller.Monet, O.G., et al. 1992, AJ, 103, 638 (M92).Monet, O.G., & MoneI, A.K.B., 1992, BAAS,

24, 1238.Ruiz, M.T., et al., 1991, ApJ, 367, L59.Tinney, C.G., 1993a, AJ, 105, 1169 (T93).Tinney, C.G., 1993b, ApJ, 414, 279.Tinney, C.G., Reid, LN., Mould, J.R., 1993b,

ApJ, 414, 254.

High-Resolution Speetroseopy at the ESO 50-ernTeleseope: Speetroseopie Monitoring of GalaetieLurninous Blue VariablesB. WOLF 1, H. MANDEL 1,0. STAHL 1, A. KAUFER 1

, TH. SZEIFERT1, TH. GÄNG 1

,

C.A. GUMMERSBACH 1, J. KOVACS2

1Landessternwarte Heide/berg-Königstuh/, Heide/berg, Germany;2Gothard Astrophysica/ Observatory, Szombathely, Hungary

Introduction

High-dispersion spectroscopy usedto be the domain of big coude spectro­graphs attached to large telescopes. Atleast since the launch of IUE it has be­come quite obvious that high-resolutionspectroscopy can be done with a tele­scope as small as 45 cm if equippedwith an echelle spectrograph. With IUEeven extragalactic objects are being in­vestigated. All known Luminous BlueVariables (LBVs) of the MagellanicClouds, for example, have been re­peatedly observed by our group in thehigh-resolution echelle mode.

For obvious reasons it is also verydesirable to use echelle spectrographsconnected to small telescopes forground-based observations. The pres­sure for observing time is much smallerthan for large telescopes and hencelong-term programmes have a betterchance of being realized if achievablewith a small telescope.

Echelle spectrographs, however, areweil known to be very sensitive to bend­ing effects. If directly attached to thetelescope, e.g. at the Cassegrain focus,

the necessary mechanical stability canbe reached only at the expense of greatweight (e.g. CASPEC of the ESO 3.6-mtelescope weighs more than 500 kg).The use of echelle spectrographs forground-based observations at small te­lescopes, therefore, used to be very lim­ited. The possibilities for doing this,however, have improved dramaticallysince the advent of optical fibers forastronomical observations.

With our fiber-linked echelle spectro­graph attached to the ESO 50-cm tele­scope we obtained unprecedented timeseries of highly resolved spectra of afew galactic LBVs and, as a by-product,of two other hot stars. A short descrip­tion of the instrumentation and of thecampaign and observational results arepresented in this report.

Instrumentation

The idea of building a compact, fiber­linked, portable high-resolution echellespectrograph was conceived in 1984and looked very promising in filling aninstrumentation gap of nearly all smaller

telescopes. The spectrograph namedFLASH (fiber-linked astronomical spec­trograph of Heidelberg) has been de­signed and constructed at the Landes­sternwarte Heidelberg (Mandel, 1988)and has subsequently been successfullyused for spectroscopic monitoring cam­paigns at different sites and telescopes.

Our equipment, comprising the spec­trograph, a TV guiding system, mechan­ical interfaces, a computer system witha magnetic tape, monitors and powersupplies with a total weight of about600 kg fits into eight medium-size con­tainers. Two well-trained people areable to install and adjust the system inless than half a day.

In practice, our spectrograph worksmuch like CASPEC with only two signifi­cant differences; the rectangular spec­trograph slit is replaced bya round fiberwith 100 Il core diameter and the spec­trograph is not mechanically connectedwith the telescope. The light scramblingproperty of the fiber results in ahomogeneous illumination of the echellegrating independent of guiding errorsand seeing variations which also sim-

19

Figure 3: Control room at astronomers office with CCD-, computer- and TV-guiding-monitor,personal computer, and magnetic tape. With this equipment we are completely independent,using only the naked telescope at each observation site.

Figure 4: Une profiles and profile variations of Sill 6347 (Ieft) and Hel 6678 (right) of AG Car.Look up table: black, blue (absorption) - green, yellow (continuum) - red, white (emission). Thefines are centred to the systemic velocity (+ 20 km S-I) of AG Car. The complete width of theabscissa is from -300 to +300 km S-I for both lines. The ordinate gives the time fromJD2449023 (bottom) to JD2449139 (top).

A quick inspection of the incomingdata has readily shown the considerableline profile variations of the target stars.This is demonstrated in Figure 4 by He I6678 (right) and Si 116347 (Ieft) of AG Garwhich had a visual magnitude of about 7during the campaign. A spectrum with aS/N ratio of about 100 in the red spectralrange was obtained in about two hoursexposure time. In the time spanJ02449023 to J02449139 we could ob­serve AG Gar in 91 nights. Figure 4exhibits the variations of the colourcoded intensity distributions of the lines.The lines are centred at the system ve­locity (+20 km S-1) of AG Gar. The totalwidth of the abscissa is 600 km S-1 forboth lines. The ordinate gives the timeinterval increasing from bottom to top.The increasing intensity is coded fromblack, blue (absorption) to green, yellow(continuum), and to red, white (emis­sion). Spline fits through the intensity ateach wavelength and resampling inequidistant time steps were used to in­terpolate for those few nights of notspectroscopic quality and to account fornot completely equal time intervals fromnight to night.

As shown by the Figure, in the be­ginning Hel 6678 showed a strong ab­sorption line at virtually systemic veloci-

that the efficient handling of the hugeamount of spectroscopic data was onlypossible due to the al ready existing far­reaching automatization of the reduc­tion procedure which is a modified ver­sion of the ESO-MIOAS echelle reduc­tion package running at the UNIX work­stations of the Landessternwarte (cf.Stahl et al., 1993a).

Results

each observer sent the OAT tapes to theLandessternwarte Heidelberg-König­stuhl, where the gathered data werefeverishly reduced. It should be noted

the ESO 50-cm telescope in periods 50and 51 to observe the establishedgalactic LBVs 11 Gar, AG Gar andHO 160529 with FLASH. The length ofthe period was motivated by the time­seales mentioned above for photometriemicrovariations for which in the case ofHO 160529 semi-periods of 57 and 101days have been quoted in the literature(Sterken, 1977 and Sterken et al., 1991).Note that the typically expected dynam­ical timescales of the extended atmo­spheres of LBVs of a few hundred solarradii during outburst are also of thisorder. ESO generously allocated the re­quested observing time fram Februarythraugh May 1993. Only 15 nights couldnot be used due to bad weather. Thecampaign has thus certainly contributedto improved statistics of useful nights in1993 at this telescope, which is normallyused for photometry only.

Fortunately, ESO has pravided travelexpenses for six observers so that theheavy burden of securing more than onethousand scientific frames could be dis­tributed upon the shoulders of severalmembers of the Wolf pack. At the end ofhis run of typically three weeks duration,

21

Figura 6: The spectacularly regular Ha-profile variations with aperiod of 15.43±0.03 days of8 'Ori C. Look up table: black (absorption - blue (continuum) - green, yellow, red, white(emission). The spectrum extends from the nebular emission (white), to -600 km S-I to the leffand to +300 km S-I to the right. The time span on the ordinate is JD2449023 to JD2449112.The curvature of the terrestric lines is again evident.

Figura 5: The dramatic Ha-profile variationsofßOri. Centre of the abscissa is the laborat­ory wavelength of Ha; the complete width isfrom -410 to +410 km S-I. Look up table asfor Figure 4. The ordinate extends fromJD2449023 to JD2449128 (bottom to top).Note the smooth curvature of the terrestriclines (indicated by arrows) due to the reduc­tion of the spectra to heliocentric velocities,which also demonstrates the accuracy of theradial-velocity measurements.

ty. A few days later an additionalfaint absorption at a velocity of about120 km S-1 and slightly later a redshiftedemission became discernible. This typeof profile was followed by an inverse PCygni-type profile after the third monthof our campaign. Finally, during the lastmonth, quite drastic changes occurredfrom an inverse P Cygni-type profile viaa double absorption to a pronounced PCygni-type profile.

The corresponding profile variationsof Si 11 6347 are less pronounced. A PCygni-type profile is prevailing with anexpansion velocity of about 100 km S-1

which agrees with the wind velocity pre­viously derived for AG Car by Wolf andStahl (1982). But the intensities both ofthe emission and absorption compo­nents vary quite considerably. Occa­sional substructures in the emissioncomponent are also discernible.

Since our spectrograms cover a largewavelength range, a number of strategicIines formed in different layers can bescrutinized and can be used to probethe time- and depth-dependent velocityfields in the atmospheres of LBVs. Theresults clearly demonstrate that thecampaign has provided a wealth of in­formation, a very good basis for a deep­er understanding of the physics of thewinds of LBVs and for modelling thehydrodynamic processes connectedwith the LBV phenomenon.

22

In addition to the galactic LBVs, weobserved the B91a supergiant ß Ori andthe 07V star 8 1 Ori C. ßOri was alwaysexposed for five minutes at the begin­ning of each night to check the setupof the equipment and to control the fo­cus of the telescape. In 86 nights(JD2449023-JD2449127) spectra weresecured. Quite interestingly, dramaticHa-profile variations ranging from in­verse to normal P Cygni-type profiles viadouble emission to pure absorptionwere observed (see Figure 5; look uptable like for AG Car). The change fromnormal to inverse P Cygni-type profilesand vice versa sometimes occurs withina few nights.

Ha emission in B supergiants is ofteninterpreted in terms of steady-statemass lass. The rapid variability of thesurface phenomena concluded from theHa variations of ß Ori, however, indi­cates that a steady-state approach todescribe these extended atmospheresand their winds is at least not a com­plete one. Allowance has to be madefor time-dependent hydrodynamic pro­cesses.

In addition, it is weil known that fiber­fed spectrographs with their lightscrambling properties allow for particu­larly precise radial-velocity measure­ments. Therefore, the set of data ofß Ori represents an invaluable treasurefor oscillation analyses and theoreticalinvestigations of pulsational motions.Such a homogeneaus set of data oversuch a lang time period and broad spec­tral range has never been obtained be­fore with modern detectors for any ofthe hot supergiants.

Again it is evident that for realisticwind models of even "normal" super­giants the impact of lang-term spectros­copic monitoring programmes is quiteessential.

Our attention has been drawn to 8 1

Ori C by Manfred Pakull. This famous07V star of the Trapezium of the Orionnebula is known to be spectroscopicallypeculiar and variable. Occasional in­verse P Cygni-type profiles of the He 114686 line had been observed and re­ported in the literature (Conti, 1972).Therefore, we put this star into the list ofour targets. In the period JD2449023 to

JD2449112 we exposed 8 1 Ori C in 89nights. The typical exposure time wasone hour. As evidenced by Figure 6, thespectrum of 8 1 Ori C is distinguished byextremely regular variations of Ha, theperiod being 15.43 ± 0.03 days (seeStahl et al. 1993b). In the Figure, thenebular emission (white) is shifted sothat a range of -600 to +300 km S-1

around Ha is displayed. Continuum isblue. Blue-shifted stellar emission andabsorption alternate very regularly withvirtually no difference from cycle to cy­cle. The apparent deviation during thefifth period is caused by worse samplingdue to bad weather. Note that the dis­cernible substructure in the blackstripes is due to a second maximum of(redshifted) emission. This same strictperiodicity was also found for Hell 4686and other different lines. 8 1 Ori C is agood example to show the importanceof having long time series with regularsampling and good resolution in time.Based on previous snap shot observa-

tions, the inverse P Cygni-type emissionof He I1 4686 "occurred on an irregularfashion" and was therefore ascribed toaccretion rather than to somethingstrictly connected to the rotation of 8 1

Ori C. The strict periodicity now estab­lished does, however, favour such aconnection and makes 8 1 Ori C thefirst convincing candidate of an 0 staroblique rotator.

Conclusion

The results presented demonstratethe considerable impact of long-termhigh-resolution spectroscopic monitor­ing programmes at small telescopes onvariable star research.

The ESO 50-cm telescope, our fiber­linked echelle spectrograph and the ex­cellent meteorological conditions of theAtacama desert - a perfect match forinvestigating the long-term spectros­copic behaviour of bright stars.

References

Conti, P.: 1972, ApJ, 170, 325.Mandel, H.: 1988, in lAU Symp. 132, eds. G.

Cayrel de Strobel and M. Spite, p. 9-13,Kluwer.

Stahl, 0., Mandel, H., Wolf, S., Gäng, Th.,Kaufer, A., Kneer, R., Szeifert, Th. Zhao, F.:1993a, A&AS, 99, p. 167-177.

Stahl, 0.: 1993, in New Aspects of MagellanicCloud Research, eds. S. Saschek, G.Klare, J. Lequeux (Proc. Sec. EuropeanMeeting on the Magellanic Clouds, SFS328), p. 263.

Stahl, 0., Wolf, S., Gäng, Th., Gummers­bach, CA, Kaufer, A., Kovacs, J., Man­del, H., Szeifert, Th.: 1993b, A&A, 274,L29-L32.

Sterken, C.: 1977, A&A, 57, 361.Sterken, C., Gosset, E., Jültner, A., Stahl, 0.,

Wolf, S., Axer, M.: 1991, A&A, 247, 383.van Genderen, A.M.: A&A, 208, 135.Wolf, S.: 1989, A&A, 217, 87.Wolf, S.: 1992, in Nonisotrapic and Variable

Outtlows trom Stars, eds. L. Drissen, C.Leitherer, A. Nota, (A.S.P. Cont. series Vol.22), p. 327.

Probing the Kinematics in the Core of the GlobularCluster M15 with EMMI at the NTTP OUBATH and G. MEYLAN, ESO

0. QUELOZ and M. MAYOR, Geneva Observatory, Switzerland

1. M15: a PrototypeCollapsed-Core Cluster?

There is now agiobai theoreticalunderstanding of the long-term dynami­cal evolution of globular clusters. Differ­ent kinds of theoretical approaches pre­dict the collapse of the cluster core,which can then be halted or even re­versed by a core heating due to stellarencounters involving binary stars. Acluster could suffer a succession of col­lapsing and expanding phases: the so­calied gravothermal oscillations (for re­cent reviews see the proceedings of theworkshop Structure and dynamics ofglobular clusters, Djorgovski and Mey­lan eds. 1993).

From an observational point of view,however, the situation is much less clear(see e.g. Meylan 1993). A major difficul­ty in finding a signature of core collapsein a globular cluster is that the observ­able structural changes may occur onlyin a very small central area, where accu­rate measurements of surface bright­nesses and velocity dispersions aregreatly complicated by the smallnumber of bright stars dominating theintegrated light. In the case of the high­concentration globular cluster M 15,

considered for a long time as a proto­type of the collapsed-core star clusters,the observational difficulties are particu­larly important.

The current determinations of the sur­face-brightness profile of M15 do notallow us to discriminate between pre­and post-core collapse models, nor toexclude the presence of a central mas­sive black hole. Although the centralluminosity cusp in M15 has now beenclearly resolved into several bright stars(see Figures 1 and 2), even the mostrecent studies from HST data cannotunambiguously determine whether thesurface-brightness radial profile flattensoff interior to a radius of about 2" orcontinues to rise at subarcsecond radii(see Lauer et al. 1991 and Yanny et al.1993). The central velocity dispersionprofile in M 15 is also poorly known.Accurate central velocity dispersionsare difficult to obtain from radial veloci­ties of individual stars because ofcrowding and the small number of brightstars. An alternative is to use integrated­light spectra to derive velocity disper­sions by measuring the line broadeningthat arises from the random motions ofthe stars. In this way, Peterson et al.

(1989) obtained velocity dispersion val­ues 8.4 :5 op:5 30.0 km S-1 over differentsmall (- 1") areas of integration in thecentral few arcseconds of M15. Theyretain as their best estimate a centralvelocity dispersion of 25 km s-\ a valuedifficult to reconcile with any existingmodel, and possibly indicative of thepresence of a central black hole. Morerecently, we derived a velocity disper­sion of 14 km S-1 from an integratedlight spectrum obtained over a centralarea of integration of 6" x 6" (Meylan etal. 1991, Dubath et al. 1993, 1994). Be­cause of our larger sampling area, weprobably would have missed any centralvelocity dispersion cusp over an area of-1". However, recent numerical simula­tions (Zaggia et al. 1992a, b, and Dubathet al. 1993, 1994) pointed out that thevelocity dispersions derived over suchsmall central areas in M15 are affectedby large statistical errors because of thedominance of too small a number ofbright stars. These errors can explainthe large variation of velocity-dispersionestimates obtained at different locationsin the core of M15.

In order to test the existence of acentral velocity dispersion cusp in the

23

Figure 1: GGO image of the centraI10.5" square region of the globular cluster M15 taken in theV-band with HRGam at the GFHT (from Racine & McGlure 1989). The angular resolution on thisimage is 0.35" FWHM. The three stars, forming an equilateral triangle at the centre of thefigure, are the main contributors to the former unresolved luminosity cusp.

2. Mapping the Core of M15with EMMI Observations

In July 1993, we obtained five high­resolution integrated-light echelle spec­tra in the core of M15. We used a 1"x8"slit, with exposures offset in 1" steps inorder to cover a total central area of5"x8" (see Figure 3). The exposuretimes were -30 minutes for each expo­sure. Ouring these observations, theseeing values (determined from EMMICCO images) were about 0.9". EMMIwas used in echelle mode with theechelle grating #10 and the cross-dis­persing grism #5 (see the EMMI operat­ing manual). The CCO used is the ESOCCO #34. It is a LORAL CCO with2048 x 2048 pixels of a size of 15 11mwhich correspond to 0.35" on the sky.For our instrument setup and slit width,the typical full-width at half-maximum(FWHM) of the emission lines of thethorium-argon comparison spectra, i.e.,our typical spectral resolution, is9-10 km s-'.

Before each exposure on the clustercore, we also obtained (1) an echellespectrum of an isolated red giantmember of M15, and (2) CCO images ofthe core of M15 in the V-band. Theobservations of red giant stars showthat the width of stellar cross-correlationfunctions is perfectly constant during allthe observations and small (6.5 km s-')

core of M15, we carried out new high­resolution observations with the ESOMulti-Mode Instrument (EMMI) on theND. The best way to minimize thestatistical error due to a small stellarsampie is to obtain a full 2-D kinematicalmap of the cluster core, i.e., to deriveradial velocities and velocity dispersionsat many different locations. The uniqueimaging/spectroscopic capabilities ofEMMI are very useful to carry out suchobservations. CCO images taken justbefore an echelle spectrum allow veryprecise a priori/posteriori positioning ofthe slit within the crowded core of M15.

•

•

•

•9

••

Figure 2: The same region of M15 as inFigure 1, as seen by the Faint Object Gamera(FOG) of the HST (Oubath et al. 1994). Thispublic image was obtained in the F/96 modewith the F342 (central wavelength 3420 A)filter. The sharp cores of the point spreadfunctions have FWHM = 0.08". No imagerestoration has been applied to this image.The three central stars are even more promi­nent at this wavelength than in the V-bandimage (Figure 1).

24

•

•

•••

•••

in comparison with the expected centralvelocity dispersion (10-25 km s-') inM15. The width of the cross-correlationfunctions of stars depends mostly,when the intrinsic width of the stellarlines is smalI, on the spectral resolutionof the observations.

The GGO images were first used toposition the slit with the usual proce­dure. A bright isolated star is accuratelycentred on the slit in echelle mode usingthe slit viewer. EMMI is switched to theimaging mode, and the position on theGGO corresponding to the slit positionin echelle mode is determined from animage of the star. The telescope is thenshifted to move the cluster location tobe observed to the same pixel coor­dinates as those of the bright star, andEMMI is switched back to the echellemode to start the spectral observation.These GGO images also allow an a pos­teriori check of the slit position. Theintensity profile through the slit is com­pared with that from the GGO image atthe expected slit location. Thanks to thecrowded stellar field in the core of M15,a good match between the two profilesis only obtained at one location on theGGO. Moving by one pixel in any direc­tion degrades significantly the agree­ment between the two intensity profiles.In this way, we can determine the posi­tion of the slit to better than half a pixel,i.e., to better than 0.2". The exact loca­tions of the 1"x 8" slit during the fivehigh-resolution spectral observationsare displayed in Figure 3.

3. Data Reduction withINTER-TACOS

Figure 3: In this figure, the HST image from Figure 2, displayed with a high low-cutoff so as toshow only the bright stars of this image as black dots, is superposed to isomagnitude contoursfrom one of the V-band GGO images taken with EMMI at the NTT. The isolated stars of theEMMI image have FWHM of 0.9". The five dashed-line rectangles show the exact positions ofthe 1"x8" s/it during the five high-resolution spectral observations on the cluster core. Thethree solid-line rectangles are three particular areas of integration for which the correspondingcross-correlation functions are displayed in Figure 4.

The data reduction was carried outwith a new software called INTER­TAGOS (INTERpreteur-Treatment, Anal­ysis, GOrrelation of Spectra) developedby L. Weber and O. Queloz at the Gene­va Observatory. This programme is builtand optimized for the automatic datareduction of echelle spectra from fiber­fed spectrographs but is also efficientfor images from slit spectrographs. IN­TER-TAGOS is now in operation at theObservatoire de Haute-Provence to doon-line the automatic data reduction ofspectra from the ELOOIE echelle spec­trograph.

This software includes a cross-corre­lation package which works easily withvery low signal-to-noise images, typical­Iy used for cross-correlation analysis.Optimal orders extraction and very effi­cient cosmic correction algorithms(Horne 1986) are available. Great carewas taken to define a good wavelengthcalibration algorithm. Using about 1000calibration lines, we measured withELOOIE at the OHP a wavelength cali­bration reproducibility of 2 m/s! The

cross-correlation algorithms work with2-D spectra (orders - pixels) and awavelength solution stored in coef­ficients. The different orders are neitherrebinned in wavelength units, normerged together.

The five echelle spectra of the clustercore were reduced by taking advantageof the spatial resolution along the slit, asfor long slit spectra. The spatial informa­tion along the slit of EMMI in echellemode is fully conserved. We checkedthis by observing isolated stars posi­tioned at different locations along theslit. In addition, with a slit of 8" in lengthand the EMMI setup used, the succes­sive orders do not overlap.

For each of the five observations inthe cluster core (see Figure 3), we ex­tracted spectra from each order in manyspatial bins along the slit direction.These spectra were then reduced usingINTER-TAGOS, and the reduced spec­tra cross-correlated with a numericalmask. The properties of this mask, asweil as the details of our cross-correla­tion technique, are described in previ-

ous studies (e.g., Oubath, Meylan andMayor 1992). Our cross-correlationtechnique produces a cross-correlationfunction (GGF) - relative intensity as afunction of the radial velocity Vr - whichis nearly a perfect Gaussian (see Fig­ure 4). The radial velocity is given by theabscissa of the minimum of the GGF,and the velocity dispersion can be de­rived from the broadening of the GGF incomparison with GGFs of individualstars.

4. Results

The radial velocity and the broadeningof the cross-correlation function werederived for each pixel position in thearea covered by the five slits displayedin Figure 3. The spatial resolution ofthese measurements is limited in onedirection by the slit width (1 ") and in theother direction - along the slit - by theseeing (-0.9"). This kinematical mapfully confirms the results of our numeri­cal simulations (Oubath et al. 1994)which predicted large statistical errors,

25

Figure 4: Cross-eorrelation funetions of theintegrated light speetra taken over three par­tieular areas of integration iIIustrated by thethree solid-line reetangles in Figure 3. TheCCF A has a stellar width and allows us toderive an aeeurate radial veloeity for the starloeated in the reetangle A in Figure 3. Thedouble CCF C shows that the two stars inreetangle C, barely spatially resolved, areelearly resolved in veloeity by our observa­tions. In the ease B, we have integrated overa slightly larger area in order to produee aCCF as large as possible. The veloeity dis­persion derived from the broadening of theCCF Bis 15 km S-l.

due to small sampies, on the velocitydispersion measurements derived fromintegrated light spectra taken over smallareas of integration atthe centre of M15.The CCFs derived at the locations of thebrightest stars are not significantlylarger than the CCF of isolated stars.Around these locations, the CCFs arebarely broadened, and any velocity dis­persion measurement derived fromthese CCFs would underestimatestrongly the real velocity dispersion. Atother locations, the CCFs are clearlydouble (or tripie) and sometimes two (orthree) spatially unresolved stars appearto be spectroscopically resolved. In

References- Auriere, M., & Cordoni, J.-P. 1981, A&A,

100,307.- Dubath, P., Meylan, G., & Mayor, M. 1992,

ApJ, 400, 510.- Dubath, P., Mayor, M., & Meylan, G. 1993,

in Strueture and Dynamies of GlobularClusters, ASP Conference Series, Vol. 50,eds. S. Djorgovski & G. Meylan (San Fran­cisco: ASP), p. 69.

- Dubath, P., Meylan, G., & Mayor, M. 1994,ApJ, in press.

- Grabhorn, R.P., Cohn, H.N., Lugger, P.M.,& Murphy, B.w. 1992, ApJ, 392, 86.

- Horne, K. 1986, PASp, 98, 609.- IIlingworth, G., & King, I.R. 1977, ApJ, 218,

L109.- Lauer, T.R., Holtzman, JA, Faber, S.M.,

Baum, w.A., Currie, D.G., Ewald, S.P.,Groth, E.J., Hester, J.J. Kelsall, 1., Light,M., Lynds, C.R., O'Neil, E.J., Schneider,D.P., Shaya, E.J., & Westphal, JA 1991,ApJ, 369, L45.

- Meylan, G. 1993, in Ergodie Coneepts inStellar Dynamies, eds. D. Pfenniger andv.G. Gurzadyan (Berlin: Springer), in press.

- Meylan, G., Dubath, P., & Mayor, M. 1991,BAAS, 23, 833.

- Meylan, G., & Dubath, P. 1993, BAAS, 23,in press.

- Phinney, E.S., & Sigurdsson, S. 1991, Nat.349,220.

- Phinney, E.S. 1993, MNRAS, in press.- Peterson, R.C., Seitzer, P, & Cudworth,

K.M. 1989, ApJ, 347, 251.- Racine, R. & McClure, R.D. 1989, PASp,

101, 731.- Yanny, B., Guhathakurta, P., Schneider,

D.P., & Bahcall, J.N. 1993, ApJL, in press.- Zaggia, S., Capaccioli, M., & Piotto, G.

1992a, in Star Clusters and Stellar Evolu­tion, eds. E. Brocato, F. Ferraro, & Piotto,Mem. Soe. Astron. /tal., 63, 211.

- Zaggia, S., Capaccioli, M., Piotto, G. &Stiavelli, M. 1992b, A&A, 258, 302.

5. Conclusion

We do not find any evidence for avelocity cusp in M15 from our mappingof the kinematics in the central areaof 5"x8". There is no evidence for acentral velocity dispersion significantlylarger than 15 km s-" and our bestestimate is op = 13±3 km S-l. This val­ue is consistent with predictions of sev­eral pre- or post-collapse theoreticaldynamical models of M15: op(O) =

12-17 km S-l from IIlingworth and King(1977), op(O) = 13-15 km S-l fromPhinney and Sigurdsson (1991) and Phin­ney (1993), and op(O) = 14 km S-l fromGrabhorn et al. (1992). Consequently,there is no need to invoke the presence ofany massive central black hole in the coreof M15.

these cases, if the few dominant starshave unusually large radial velocitydifferences, the CCFs are artificiallybroadened leading to overestimates ofthe velocity dispersion. These differentcases are illustrated in Figure 4, whichshows three CCFs A, B, and C obtainedrespectively from the area of integrationA, B, and C displayed in Figure 3. TheCCF A has a stellar width and allows usto derive an accurate radial velocity forthe star (AC 212, Auriere and Cordoni1981) located in the rectangle A in Fig­ure 3. The double CCF C shows that thetwo stars (AC # 214 and # 215) inrectangle C, barely resolved under theseeing conditions during the observa­tions, are clearly resolved in velocity.Accurate radial velocities were also de­rived for these two stars. In the case B,we have integrated over a slightly largerarea in order to produce a CCF as largeas possible. The velocity dispersion de­rived from the broadening of the CCF Bis 15 km s-" however, the statisticalerror on this result is large since the CCFB includes mostly the contributions ofthree stars. This is not obvious fromFigure 4B, but appears unambiguouslyin CCFs obtained over smaller spatialbins.

The broadening of the cross-correla­tion functions is always :5 17 km s-" atany location in the 5" x 8" central areamapped. Gur numerical simulationsshow that this value provides very prob­ably an upper limit for the central veloci­ty dispersion. The CCFs of integratedspectra taken at locations away fromthe brightest stars are less affected by'statistical errors due to small sampiesand give velocity dispersions 10:5 op :515 km S-l. In order to minimize thestatistical error due to a small sampie,one can reduce the domination of thefew brightest stars by taking the aver­age of the normalized CCFs over alllocations in the 5" x 8" central area. Inthis way, a velocity dispersion of11.7 km S-l is derived.

The radial velocities of the 14 bestresolved (spatially or spectroscopically)bright stars were also determined. Thevelocity dispersion from these stars is16.0 ± 3.0 km S-l. This value is alsolikely to be an upper limit, since starswith large relative velocities are moreeasily spectroscopically resolved. Wehave radial velocities for two of the threebrightest stars (AC # 214, 215, 216, thethree bright stars in the centre of Fig­ure 1 and 2) of the former unresolvedcusp, the third being too blue to providea radial velocity. Two of the brighteststars, separated by 2.5", AC # 212 and215, have radial velocity values differingby 48.9 km S-l. Abrief account of theseresults is published in Meylan andDubath (1993).

c

A

B

100.........~........

99>,::::rnt::III 98.....t::

97

100.........~........

99>,::::rnt::III 98.....t::

97

100

.........~........

99>,.....'Ujt::III 98......s

26

A New Quasar Pair: Q2126-4350 and Q2126-4346M.R.S. HAWKINS, Royal Observatory Edinburgh, Great BritainR. W HUNSTEAD, School of Physics, University ofSydney, AustraliaG. MEYLAN, European Southern Observatory, München, GermanyP VERON, Observatoire de Haute-Provence, FranceS.G. OJORGOVSKI, S.G. and J.D. SMITH, Division of Physics, Mathematics and Astronomy,Caltech, Pasadena, USA

Wavelength (A)

Figure 2: Spectra of the two quasars observed withEMMI. Top: 02126-4350, bottom: 02126-4346.

9000

='0 -C 0ca ~.0q;

7000

'0Cca.0

lIJ

6000

are two images of a single quasar, thesedifferences could perhaps be due to thetime delay between the two light paths.

The whole 19-deg2 field of our vari­able quasar search has been surveyedat 843 MHz with the Molonglo Observa­tory Synthesis Telescope (MOST) (Mills,1981). One member of the new quasarpair (02126-4346) is a strong radiosource, with a flux density of 178 mJy,whereas the other quasar (02126-4350)is not detected at 843 MHz, having a 30upper limit of 2.5 mJy. Furthermore,02126-4346 is not detected in the PNMsurvey at 4850 MHz (Gregory et al.1993), implying that the source is weak­er than 45 mJy at this frequency andtherefore that it has anormal spectrum(a<-0.8) and is unlikely to be variable.Consequently, the radio information al­most certainly excludes the hypothesisthat we are looking at a gravitationallylensed system and reinforces the ideathat quasars cluster on a scale -1 Mpc.

ReferencesBlandford, R.D., Phinney, E.S. and Narayan,

R. 1987, ApJ 313, 28.Gregory, P.C., Vavasour, J.D. and Scott,

W.K. 1993, NRAO preprint.Hawkins, M.R.S. and Veron, P. 1990, The

Messenger 61, 46.Mills, B.Y. 1981, Proc. ASA 4, 156.Phinney, E.S. and Blandford, R.D. 1986, Na­

ture 321, 569.Turner, E.L. et al. 1986, Nature 321, 142.

In the course of a survey for opticallyvariable quasars (Hawkins and Veron,1990), we have found a new pair ofquasars (02126-4350 and 02126-4346)with similar redshift (z-1.10) and sep­aration (202 arcsec) to 01146+111.These two objects have about the samemagnitude (B=20.2 and 20.4 respec­tively on the reference UKST Schmidtplate). Both have a high amplitude ofvariability, AB = 1.0 mag. We have deter­mined that, in our sampie, -8 % of allUVX quasars have such a high am­plitude of variability; this fact suggestedto us that, in this case, we were possiblyobserving a large-separation gravita­tionally lensed system.

A 60-min exposure spectrum wasobtained on August 18, 1993 with theEMMI spectrograph at the ESO ND3.5-m telescope (shown in Figure 2).The two objects were placed simultane­ously on the slit. The stronger object(02126-4350) shows a broad Mg 11emission line and a narrow [Oll] emis­sion line allowing to determine an accu­rate redshift z= 1.116. The fainter objecthas only a broad Mg 11 emission line atthe same redshift. The two spectra looksignificantly different, but if the objects

A..• •

Figure 1: Part ofa; 2-minute exposure

.. • frame taken on~. August 18, 1993

B • through a I filter with. EMMI at the ESO

• ~ • NTT on La Silla. The.. • size is 3.9 arcmin x4.7 arcmin. North is

• up, east to the left.• The seeing is 1.4 arc-

-- sec. The two

0- • quasars, 02126-4350 and 02126- )(

::J

4346, identified with ;;::

, ... the letters A and B,Q). .~..

respectively, are <ii.. Q;

• separated by 202 a:

arcsec.

..•

Since the discovery in 1979 of thefirst gravitationally lensed quasar00957+561, a lot of effort has beendevoted to finding more such objects.Twelve are now known, the largest sep­aration between the various images be­ing 6.5 arcsec.

However, neighbouring quasars hav­ing the same redshift are not necessarilyimages of a gravitationally lensed sys­tem. Six pairs of quasars have beenfound with separations in the range 3 to10 arcsec corresponding to a few tensof kiloparsecs. These objects are be­lieved to belong to the same group orcluster of galaxies.

Another pair of quasars, 01146+111Band C, at z= 1.012, with aseparationof 157 arcsec, attracted a lot of attentionsome time ago. Turner et al. (1986) havesuggested that this is a single quasargravitationally lensed by a massive clus­ter of galaxies. Blandford, Phinney andNarayan (1987) have shown that thisassumption is very unlikely to be correctand Phinney and Blandford (1986) havesuggested that 01146+111 Band C aretwo distinct quasars separated by ­700 kpc whose proximity is attributableto clustering.

27

OTHER ASTRONOMICAL NEWS

VLT Working Group for Scientific Priorities ­Status of the WorkL. V/GROUX, Service d'Astrophysique, Sac/ay, France

In its May 1993 session, the ESO Sci­entific and Technical Committee formeda working group to propose a set ofmain scientific priorities to serve asguidelines for future discussions on theVLT and its instrumentation. A numberof working groups on this matter existedduring the early definition phase of theVLT. Their reports are included in theproceedings of the 2nd VLT Workshop,held 1986 in Venice. On that basis, ESOworked out the VLT InstrumentationPlan which was widely circulated in thecommunity in June 1989 and discussedby ESO committees. Between the pre­paration of the Blue Book and the com­missioning of the first unit telescope,about 12 years will elapse - even morefor the other unit telescopes. Beingroughly half-way between these twoevents, the STC thought it timely to re­assess these scientific priorities for theVLT and the instrumentation plan, takinginto account recent scientific and tech­nical developments. Another goal of thisexercise is to provide scientific prioritieswhich can later be used as guidelines inprevision of future problems, technicaltrade-off or descoping.

After some changes during the sum­mer, the group is now composed of STCmembers K. de Boer, B. Marano and L.Vigroux (chairman). ESO represen­tatives J. Wampler, J. Walsh and S.D'Odorico and two external experts, B.Fort and R. Kudritzki.

To involve the ESO community in thisactivity, we circulated during the sum­mer a questionnaire about the scientificprogrammes to be done with the VLT.The real work of the group started inSeptember 1993. The main line of ourreflection is organized around severalsteps:• review the capabilities of other obser­

vatories in the VLT era, both onground and in space. Scientific pro­grammes for the VLT have to be ex­amined in the context of what will bedone at the other observatories,

• assess the uniqueness of the VLT,both as single 8-m telescope or withthe four telescopes,

• define a set of scientific domains inwhich the VLT with an appropriateinstrumentation will have the

28

capabilities to create a unique break­through,

• make recommendations in severalareas of the VLT: telescopes, detec­tors, instruments and operations.The first part of this work is now com-

pleted. Preliminary versions of the otherpoints have been presented and dis­cussed during the November 1993 STCmeeting. We do not yet have a detailednew instrumentation plan, but we arealmost getting there. I will indicate hereonly the general directions to get aflavour of our work.

To define the scientific priorities, wehave not tried to make an extensivesurvey of all the astrophysical problemswhich can be tackled with the VLT, butrather to focus on a few scientific do­mains in which we expect that the VLTwill provide a significant gain over exist­ing capabilities. For the time being, wehave selected four domains, star forma­tion and young stellar objects, starburstgalaxies and active nuclei, formationand evolution of galaxies, and formationand abundances of the elements. Foreach of these themes, we have iden­tified programmes which can be donewith the planned instruments, and thosewhich require new instruments. Thispart of the work must be followed in twodirections, elaborate on these themes,and incorporate one or two additionalthemes.

For the telescopes and the instru­ments, we have agreed on two maindirections: emphasize the importance ofthe infrared, and the need for very largedetectors.

Arguments for supporting infraredwork on the VLT are overwhelming. In­frared astrophysics deals with crucialareas such as star-forming regionswhich are generally embedded in dustyclouds and accessible only in infrared, ordetection of very distant galaxies whichare about 5 to 10 times brighter in theinfrared than in the visible. The largestgain provided by large telescopes is forinfrared wavelengths where observa­tions are limited by the background. Inthis case, the sensitivity increases as D4

,

D being the telescope diameter. In addi­tion, a revolution in IR detectors is nowtaking place. We should expect aboost

of IR observations similar to the drama­tic developments of optical observa­tions coincident with the use of 2D elec­tronic detectors 25 years ago. Newtechniques of imaging at the diffractionlimit with adaptive optics or interferome­try are already operational in the in­frared , but might not become availablein the visible in the next few years. To­gether with the detector revolution andthe increase of telescope size, they willprovide an enormous gain in sensitivityfor point source observations. Last butnot least, the VLT will become opera­tional after the ISO mission which isexpected to create a scientific break­through with its sensitivity improved bya factor of 50 to 100 over IRAS. Newscientific problems will be uncoveredand will require new sets of infraredobservations.

The present VLT instrument packageis designed around CCDs that are aboutstate-of-the-art at the present day. Re­cent developments in the CCD mosaictechniques and progress of the IRarrays will allow a new instrument de­sign, with a good image sampling on alarge field. The VLT has been optimizedfor image quality, and the pixel samplingmust be optimized accordingly. How­ever, further analysis is needed toassess these instrument concepts.

During the last STC meeting, it wasdecided to continue this work along theline defined in the preliminary report.ESO will strengthen its participation,both in scientific priorities definition, andin the assessment of the new instrumentconcepts. A final version of the reportwill be presented at the next STC meet­ing in May 1994 and discussed morewidely in a workshop which will beorganized by ESO before the summer.

Working Group tor Scientitic Priorities tor La SillaOperationsJ. ANOERSEN, Chairman, ESO-STC

Preparation of the Report

At its first full meeting in May, the WGemphasized the importance of receivingfeedback and advice from the commun­ity. Since then, a total of three draftreports have been widely circulated, thelast two through the members of theSTC and Users Committee. The WGalso met with the UC, on September 16.The resulting numerous comments haveall been considered in the preparation ofthe final Report, dated October 23,which was submitted to the STC at its34th meeting, November 4-5, 1993.

The STC supported the basic propos­ais of the Report and encouraged theDirector General to implement them "ingood spirit". With this recommendation,the WG has forwarded its report to theDirector General and Council for furtheraction.

The Report of the WG is freely avail­able from ESO (Section Visiting As­tronomers), and readers interested inthe details are encouraged to consult it.The following is just a brief summary ofthe rationale for its recommendations,and of some lessons learned.

Background

The La Silla Observatory will, for atleast another decade, remain the breadand butter of ground-based Europeanobservational astronomy in the southernhemisphere. Currently, La Silla is prob­ably unsurpassed for the range and flex­ibility of its facilities. Basically, VisitingAstronomers evAs) can expect to usefront-line instrumentation covering therange from the atmospheric cutoff tomillimetre wavelengths, with few otherrestrictions than the competition for ob­serving time. In addition, La Silla hosts anumber of more specialized experi­ments not directly related to the re­search conducted by ESO staff as­tronomers or VAs.

However, in recent years, new tele­scopes and instruments have appearedon La Silla at an accelerating rate, withno corresponding increase in the staff.Particularly after the advent of the ND, itis proving impossible to adequately sup­ort all the facilities currently offered tovisiting astronomers. Several changesand upgrades at the larger telescopes re­main to be fully tested and implemented.

An overload of conflicting demandsand a lack of clear priorities haveprevented the staff from addressing

these problems in a systematic way. Asa result, the scientific productivity of LaSilla's telescopes - even some of thenewest and most powerful - is beingcompromised. Clearly, this state ofaffairs cannot be allowed to continue.

Yet, with the VLT project on its hands,it is difficult for ESO to boost La Silla bynew recruitment or by drawing onGarching staff. Bringing the top-priorityfacilities up to standards worthy of aworld-class observatory must happenwithin an essentially constant staff andbudget envelope.

It follows that increased effort in someareas will draw resources from others:Quality must be enhanced at the ex­pense of quantity. In order to thus qual­itatively enhance the scientific produc­tivity of La Silla within the existing means,a set of scientific priorities for the opera­tion of the observatory are needed.

In order for ESO to steer through thisprocess in a responsible and transpar­ent manner, the Director Generalappointed in early 1993 a WorkingGroup on Scientific Priorities for La SillaOperations. Its members are: J. Krautter(OPC), J. Lub (UC), M. Mayor (ex-STC),and J. Breysacher, D. Hofstadt, J. Mel­nick, and J. Wampler (all ESO statt), withthe writer as Chairman. The proposalsof the WG were to be submitted to theDG with the comments of the STC.

Defining Scientific Priorities

While never trivial, it is relatively easyto agree on priorities for exciting newopportunities. It is far more difficult tochoose which facilities and freedomsmay have to disappear in order for LaSilla as a whole to perform optimally.Scientific priorities have not previouslybeen formulated in a way suitable forthat purpose. This is clearly reflected inthe comments received from users:about 99 per cent emphasize the uniquevalue of a particular piece of equipmentas seen in isolation, but without regardfor the entire picture.

As guidelines for its own discussion ofpriorities for instruments, services, andscheduling techniques, the WG usedthe following criteria. The list below isindicative, but neither complete nor instrict order of importance:- Uniqueness, on an international

scale, of the scientific opportunitiesoffered: La Silla belongs at the fron­tiers of astronomical research.

- Direct relevance for the VLT project.

ESO's resources, and the credibilityof the ESO community, are largelytied to the timely and successful com­pietion of the VLT. Early experienceon how to control, equip, staff, andoperate the VLT is crucial.

- Long-term importance for a broadsegment of the user community. ESOwas created to serve the scientificinterests of the community andshould provide optimum conditionsfor its top-priority research projects.

- Importance for specific interests ofuser communities in the memberstates, at a support level consistentwith the importance of the researchand the size of the community.When considering a specific facility,

the WG consulted the statistical infor­mation available from the OPC on thenumber, rating, and approval rate of theproposals received. Individual proposalratings are, of course, confidential, butaverage grades and general trends wereavailable.

Proposed Improvements

The clear top priority for increasedsupport is the ND: This telescope mustnow be brought to technical and opera­tional standards at which its great scien­tific potential can be realized. Moreover,valuable experience can be gained forthe VLT project by upgrading andoperating the ND according to VLTstandards. ESO is al ready planninghow to achieve these goals by con­certed action from La Silla and Garch­ing. The WG strongly welcomes thisinitiative.

Second priority is to bring the othermajor telescopes to consistently highperformance, especially as regards im­age quality. Items include fast and reli­able top-end exchanges and mirrorrealignment (3.6-m and 2.2-m); im­proved dome seeing; and a new controlsystem at the 2.2-m for optimum IRperformance. A full complement ofmodern CCD detectors and on-line datareduction facilities are urgently neededat all telescopes.

First among third-priority items is apermanent CAT-CES optical fibre link:The CAT M3 drive is becoming increas­ingly unreliable. Improved measure­ments of seeing and other meteorologi­cal data are also high on this list. Finally,numerous improvements of individualtelescopes and instruments are pro­posed throughout the report.

29

Proposed Economy Measures

A recommendation for increasedpriority also implies an identification ofother areas where a corresponding re­duction of effort can be made. Minor,cosmetic measures will not lead to sig­nificant overall relief, nor can a singleradical measure do so at a scientificallyacceptable cost. Hence, the recommen­dations of the WG have considered abroad range of actions.

Much of the workload on the staff isdue to frequent instrument changes.Hence, the WG proposes a systemof block scheduling on all telescopeson which the instrument configura­tion cannot be frozen entirely. Serviceobserving would be introduced asa serious option. Test and setup timecan be minimized as part of the bene­fits.

In parallel, a balanced plan is pro­posed (summarized in Chapter 6 of theReport) to redistribute the instrumenta­tion among the telescopes so that max­imum specialization is achieved at eachtelescope while limiting the total choiceas little as possible. Rare exceptionswould still be allowed.

Finally, the WG recommends that afew facilities be decommissioned as nolonger competitive on the basis of quali­ty of the data, quality and quantity ofrecent proposals, and operational andmaintenance effort. In addition to a fewinstruments, this category includes theSchmidt telescope (as a general userinstrument), the GPO, and ESO use ofthe Danish 50-cm telescope.

Lessons Learned

Most reactions to these proposalshave shown real understanding of thefactual situation: Despite very difficultfinancial conditions in most of themember states, ESO is neverthelessallowed to proceed with the construc­tion of our most coveted tool: The full­scale VLT - the world's largest tele­scope. Looking at the fate of some otherlarge research projects in the world, it isnot unreasonable that we contribute bytrimming some of our lower-priority ac­tivities.

Other comments have taken the formof unconditional demands for continuedsupport for this or that favourite facility,regardless of the impact on the rest ofESO. Few of us are in a position to makesuch demands in our home countries,and even powerful rhetoric cannot byitself make staff and money appear.

The central message of the report isthat ESO is now finding itself in the realworld of limited resources, and we haveto respond rationally to this discovery.This includes the ability to assign priorityto certain overall scientific goals in along-term strategy, and to programmeresources so as to actually achievethem. Demands for wholesale perfec­tion beyond ESO's means are basicallypointless and lead instead to generaldissatisfaction.

Longer-Term Prospects

Human beings are imperfeet, andconditions change. The WG therefore

strongly emphasizes that the task is notfinished with the present report: Re­views of operating modes and adjust­ment of the facilities offered must be­come a permanent (e.g. annual) featureof ESO's forward planning.

The compromises reached can neversatisfy everybody. The inevitable dis­satisfaction of some is best turned intoproposals for future improvements. Itsleast constructive expression would beto criticize those on La Silla who arecharged with the execution of thesenecessary policies.

A final important lesson from thiswork is how little even relatively majorrestructuring of the observing facilitieson La Silla and the way they arescheduled results in measurable effectson the total workload of the T.R.S. De­partment, let alone on the budget ofESO/Chile as such. For the longer term,this exposes again painfully clearly howsmall a fraction of the total effort andbudget of ESO has direct impact on thescientific productivity of the La Silla Ob­servatory.

It follows that when further efficiencymeasures become necessary in 1996,mere reduction of scientific oppor­tunities along the course explored here,leaving the organization itself un­touched, is not the appropriate startingpoint for a rational solution.

Profound reorganization of the entireESO infrastructure in Chile will beneeded in order for La Silla and Paranaltogether to serve the ESO community ina scientifically competitive and cost­effective way in the VLT era.

Proposal StatisticsJ. BREYSACHER, ESO, and J. ANOERSEN, Chairman ESO-STC

In the following figures, the number of observing proposals received (dotted lines) and accepted by the OPC (full lines) isplotted for each telescope/instrument combination as a function of the ESO period number. The data cover Periods 41 through52 (1988-1993).

These statistics were prepared for the Working Group on Scientific Priorities for the La Silla Operations.

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The 93NOV Release of ESO-MIDASESO Image Processing Group

The new release of ESO-MIOAS con­tains a substantial number of improve­ments and new features. Among theseis the implementation of a new set ofGraphical User Interfaces based onOSF/Motif, wh ich makes the usage of anumber of application packages easier.In the sections below the main improve­ments are highlighted. For more detailedinformation we refer to the last issue ofthe ESO-MIOAS Courier (July 1993).

1. New Features and ApplicationPackages

1.1 System

Significant modifications and en­hancements have been implemented inthe MIOAS Command Language, e.g. animproved debugger for MIOAS pro­cedures, more robust error handling anddirect access to all data structures fromwithin a procedure. To improve the in­formation transfer, the support of helptext for descriptors in data files hasbeen added. A prototype of communi­cation protocols has been implementedto enable interaction of any stand-aloneprogramme with MIOAS.

1.2 Oata Organizer

A new application package called 00(Oata Organizer) for preparation of data

reduction procedures has been im­plemented. The Oata Organizer uses asinput a list of FITS files or MIOAS imagesas weil as a list of FITS keywords orMIOAS descriptors which are consid­ered to be relevant (e.g., exposure time,telescope setting, instrument mode) tocreate an Observation Summary Table.

Each entry of this table is thenclassified according to a set of user­defined rules: the user may for instancegroup the data according to the expo­sure type and put together all framesobserved in a given instrument mode.An interface based on the Table Editorhas been developed to facilitate the for­mulation of these rules.

The association of science frameswith suitable calibration exposures isachieved by using the same rule­generating interface as referred toabove even though the rules to be ap­plied are different: One may want forinstance to look for all the Flat Fieldswhich have been taken within a certaintime interval of the science exposure.The Association Process creates aMIOAS table which can be used by anyreduction package. It contains one col­umn for each type of exposure (e.g. SC,BIAS, OK, WCAL), while each row con­tains for the corresponding science im­age the set of suitable calibrationframes.

The Oata Organizer has been tested

on the ESO Archive which contains sofar 30,000 EMMI/SUSI exposures. Thisversion of the package is still a prelimi­nary version and the structure of theoutput association table may bechanged in the future.

1.3 eeo Package

Since the last update of the MIOASCCO package in 1986 a number of newinstruments have been installed on theLa Silla Telescopes. In addition, newCCOs became available offering largepixel areas and higher quantum efficien­cy. With these innovations the variety ofobserving modes has grown and, as anobvious consequence, the amount andthe diversity of data taken have dramati­cally increased. It is clear that theMIOAS CCO reduction software shouldbe able to cope with these improve­ments and hence requires compatibilitywith the hardware as it exists at present.

When designing the basic layout ofthe CCO software, a number of basicrequirements were kept in mind: e.g.robustness, user-friendliness, easyadaption for new or non-ESO in­strumentation, automatie calibrationprocedures to enable a quick-look facili­ty at the telescope. In what sense theserequirements can be realized dependson the data-acquisition system, archiv­ing and, obviously, the data-reduction

33

system. In this respect the developmentof the CCO package took place at theright time. The ESO archive project hasaccomplished that for a number of tele­scopes and instruments the setupspecifications are stored together withthe data. In addition, the new MIOASOata Organizer package offers a signifi­cant help in preparing the data for re­duction (see above).

The new CCO package in MIOASmakes use of the output MIOAS table ofthe Oata Organizer package that con­tains the science and calibration dataand the relation between these two. Thepackage provides commands to do thevarious bias calibration steps like com­bining calibration frames, subtraction ofthe bias level determined from the over­scan area or from a separate bias frame,correction for dark current, division bythe correction for illumination, andcorrection for the fringe pattern. Also,tools are provided for trimming theframes of the unwanted over-scan strip,and for correcting the frame for badpixels intensities. All operations stepsthat successfully finished are recordedin the descriptor of the reduced frame.This recording, which includes updatingthe HISTORY descriptor, avoids repeti­tion of reduction sequences, and pro­vides the user with the information onwhat has been done to the data.

By combining the basic reductionsteps, a complete reduction pipelineprocedure is built that enables the userto do an automatie reduction of all sci­ence frames. The pipeline procedure iscontrolled by a set of reduction key­words in combination with the informa­tion stored in descriptors of the dataframes. Therefore, apart from com­mands that do the actual work, anumber of commands help the user tomanage keywords and descriptors.

1.4 Spectroscopy Packages

The long-slit spectroscopy packageLong has been totally refurbished sincethe version 92NOV. It includes all func­tions of the previous packages Spec,

Long and XSpectra as weil as manyadditional features, such as batch re­duction. The Long package nowsupports 10 and long-slit spectroscopyand includes a graphical user interface.A tutorial (command TUTORIAULONG)demonstrates the commands of thepackage.

A new package for spectral analysishas been developed by Juan Veliz at LaSilla and is based on the graphical userinterface XAlice. It provides basic func­tions for:• flux integration, including continuum

fitting and determination of line para­meters like fwhm, equivalent width,flux and continuum level

• rebinning (Iogarithmic, frequency,red-shift)

• filtering by smooth or median filters• multiple-component fitting by a set of

gaussians.

2. Graphical User Interfaces

The version 93NOV includes fourOSF/Motif based interfaces:1. XHeip provides access to the on-line

documentation. More functions havebeen implemented since the 92NOVversion, including a history mechan­ism, strings search, files printing, con­text selection and feedback (problemreport).

2. The new interface XOisplay imple­ments a number of display relatedcommands. It enables manipulationof images, LUTs, Ins and cursorcommands in an easier way.

3. The interface XLong is related to thenew long-slit spectroscopy packageLong. The interface allows the activa­tion of calibration commands andprovide convenient panels for arelines identification and batch reduc­tion.

4. The interface XAlice is related to thenew spectral analysis package Alice(see Spectroscopy Packages).All these interfaces conform to the

ESO GUI Common Conventions whichdefine the Look and Feel for all ESO

interfaces in the fields of telescope andinstrument control, archives and dataanalysis. In addition to the OSF/MotifXHeip interface, the 92NOV release in­c1uded several Athena-based interfaces(XSpectra, XEchelle, XFilter, XStella).Some of them (XEchelle, XFilter, XStella)have not yet been ported to OSF/Motifand compiled versions for Sun and HPwill be available through our anonymousftp account.

3. Availability

The 93NOV release of MIOAS isscheduled for distribution in Oecember1993. An alpha version was frozen inJuly and tested internally. After this test,the beta version was sllipped to morethan 15 sites representing the majorhardware platforms. Based on thesetest reports, the release will be finalizedin November. The 93NOV MIOAS re­lease will be verified on the followingsystems: SUN SPARC Solaris 1.x and2.x, HP 9000, IBM PS/6000, OEC Ultrix­(MIPS), OEC VAXNMS, OEC Open VMS(APX), Silicon Graphics and PC/Linux.OEC OSF/1 systems are not yetsupported but a beta-test version is ex­pected to be available in the spring of1994. Sites must explicitly request therelease, specifying the medium.

The MIOAS system is, at the moment,distributed free of charge to non-profitresearch organizations. They must signa User Agreement with ESO in order toobtain the system. Information and re­quests for MIOAS should be directed tothe Image Processing Group at ESO,Karl-Schwarzschild-Str. 2, 0-85748Garehing, Germany, or through E-mail(Internet: midas eso.org). A Hot-lineservice is also available at the sameaddress. New releases and patches canbe copied from the midas account onthe Internet host 'ftphost.hq.eso.org'.Application packages and documenta­tion are also available on our anonym­ous ftp account. A bulletin board can beaccessed through the 'esobb' accounton the Internet host 'bbhost.hq.eso.org'.

An ESO-MIDAS Implementation for PC/LinuxC. GUIRAO, ESO Image Processing Group

It may seem to be a contradiction toimplement a large image processingsystem like ESO-MIOAS on PC typesystems; however, they are becomingsurprisingly powerful. Although normalreduction of data is better performed on

34

workstations, the final analysis, whichrequires much more time for the in­terpretation of data than for actual com­puting, may be weil suited for a PC. Oneof the main objectives is to provide anESO-MIOAS implementation on a very

inexpensive system that small institutesand even individual scientists canafford.

We decided to focus on Linux, a pub­lic domain Unix system, as the mostsuitable for the MIOAS community.

Hardware Software

i4860X/25 Linux SLACKWARE 2.01 0.99.pI1220 Mbytes RAM ce: GNU compiler 2.4.5 (included)Adaptec 1542B SCSI board f2c: f77 to C translator 22 (included)1 Gbyte SCSI hard disk X11 R5 (included)WO-8013 Ethernet board Motif 2.1 (not required)Local Bus S3 Video Card MIOAS beta-release 93NOV (28 Mbytes)

Linux not only satisfied the requirementsto install MIDAS (C and Fortran compil­ers plus X11) but it also complies withANSI-C and POSIX standards. In addi­tion, it includes all the network softwarenecessary to integrate the PC into aLAN. Linux is supported by the FreeSoftware Foundation which also pro­vides other public domain software (IikeGNU).

The popularity of Linux has increasedenormously in the last months (as indi­cated by the "Iinux" newsgroup, one ofthe most active newsgroups onUSENET), and with it the interest of theAstronomical community for havingMIDAS ported to it. This became appar­ent during the 5th ESO/ST-ECF Data Anal­ysis Workshop where the MIDAS Groupshowed the progress with PC port.

Now, the situation has improved sub­stantially and we are glad to announcethat the complete "core" of MIDAS hasbeen successfully implemented andverified on Linux SLACKWARE 2.01.Some other MIDAS packages have alsobeen tested by their authors (IikeWAVELET, PEPSYS, ECHELLE andLONG). Apre-release of the 93NOV re­lease has already been distributed toseveral test-sites for a complete check­out.

The Graphic User Interface (GUI)packages for MIDAS are being ported toLinux. Two of them, XHeip and XDis­play, are al ready available while the restwill follow soon. The MIDAS GUls arebased on OSF/Motif wh ich is a licence

Table 1: Configuration of PC test system.

produce not included in the distributionof Linux. Thus, we can only distributethem in binary executable form as anoption in the distribution tape. They willalso be available under our "anonymousftp" account.

The hardware and software config­uration for the test system is given inTable 1 for information only. It does notmean to be the unique or minimumhardware setup. MIDAS requests only a386 CPU, Linux release 0.99p112 orhigher, a minimum of 16 Mbytes ofmemory and some disk space depend­ing on the amount of data needed. Withshared libraries, the MIDAS executablesand help files take around 30 Mbytes.

Table 2 gives a comparison of theperformance of some MIDAS tasks on aPC and SPARCstation 2. It should benoted that on Linux there is no realFortran compiler but a Fortran-to-Ctranslator, and access to the disk onSPARCstation 2 is about 5 times fasterthan on our PC.

Both SunOS and Linux used the

MIDAS shared library. The C-Whetstonebenchmarks by H.J. Curnow and BAWichman (1976, Computer Journal, Vol.19, No. 1) were used to compute the"cwhetstones". The last columns withMIDAS benchmarks refer to the filtertmedian command executed on a1000 x 1000 image and the Wavelettutorial written 100 % in C code.

Besides the official distribution ofMIDAS in source form, we intend tomake a fully installed version for Linuxavailable on the midas ftp account. Itwill be located in a subdirectory called"Iinux" and be available in two forms:one with sources (= 60 Mb) and anotherwith only binaries (28 Mb), all packagesincluded.

In order to limit our administrationaloverhead, we will not distribute theESO-MIDAS PC/Linux version to indi­viduals but only to registered sites.Thus, we will give MIDAS site managerspermission to distribute PC versions ofMIDAS to people associated with theirinstitute.

Table 2: Performance of MIOAS on a PC/Linux system.

System Core install Size of core Cwhetstones Filter Wavelet

PC/Linux, i4860X/25 49min 11 Mb 10 MIPS 2435 sec 313 secSUN SPARCstation 2 30min 26Mb 10 MIPS 2045 sec 405 sec

DDS/DAT Tape Cartridges as New ESO Tape Standardo. HOFSTAOT, J. MELNICK, P. GROSB0L, ESO

The 9 track W' tape format has duringthe last many years proved to be a veryreliable tape standard for the exchangeof data. Its main disadvantages arethe relatively small data capacity pervolume (approximately 200 Mbyte for a2400-foot tape written with 6250 bpi)and very bad data density in terms ofGbyte per volume or mass. Large CCDdetectors can now easily produce over a

Gbyte of data per night. These factsdemand that a new standard for dataexchange must be adopted to facilitateeasy transport of data acquired at LaSilla.

Several aspects must be consideredwhen choosing a new standard. Themedia must be reliable both in the senseof data security and with regard tosupport from multiple independent ven-

dors. Its total storage capacity and datadensity are also important factors. Datatransfer rates and speed of positioningon the media should be considered.Since many user sites would need topurchase devices for the chosen media,the price of both media and drivescannot be disregarded. A crude com­parison of different media is given in thetable, where values for the relative cost

35

Media Capacity Density Cost Speed

Gb Mb/g Mb/cm3 media drive rate forward

'12" 0.2 0.2 0.1 1 12 0.8 92MO-disk 0.6 3.1 2.8 7 4 1.4 1CD-ROM 0.6 5.7 3.3 1 (20) 0.4 1OIC 1.0 3.7 2.7 3 1 1.0 380:DDS/DAT 2.0 47.6 27.8 1 3 0.5 10Exabyte 5.0 64.9 35.8 1 4 0.5 15

and speed are only indicative. The "for­ward" speed indicates the time for a fastforward positioning on a file and de­pends on the size of the files beingskipped. CD-ROM was included forcomparison only since it is a read onlymedium. Drives for writing CD-ROMsare becoming available but are stillrather expensive as shown in the table.

Weighing the different factors, theDDS/DAT tape cartridge seems to bethe better choice. A main point is thevery good operational experience withDDS/DAT tapes used during the lasttwo years for transferring data from theND to the ESO archive in Garching. Ithas reasonable storage properties andis supported by multiple independentmanufacturers. The lower price for

drives and a relative fast positioning onfiles are also important factors.

Thus, the DDS/DAT tape format isadopted as the new standard for exportof data from La Silla. Hardware com­pression is not used since a commonstandard has not been defined for this

medium. It will still be possible for usersto request their data on W' tapes but bydefault DDS/DAT tapes are provided.The Exabyte format is also available butusers who want their data on thismedium must perform the copyingthemselves.

ESOIOHP Workshop on Dwarf GalaxiesFrom September 6-9, 1993, more

than 90 astronomers from all over theworld met at the Observatoire de Haute­Provence (OHP) for a workshop on"Dwarf Galaxies" jointly organized byESO and OHP.

Dwarf galaxies are inconspicuous,faint and small stellar systems which,until recently, have largely been ne­glected. The much rarer giant spiralsand ellipticals, more visible, attract moreattention. This is mirrored by the factthat there have been only two meetingson this subject before, one in 1980, or­ganized by ESO in Geneva, and one in1985 in Paris, organized by the Institutd'Astrophysique.

Today, dwarf galaxies are recognizedas prime laboratories for the study ofsome of the most burning issues of as­tronomy, such as structure formation,galaxy evolution, star formation, anddark matter. The number of workers inthe field is growing very rapidly. Theresponse to the announcement of thepresent workshop was accordinglylarge. This clearly shows the need formore meetings on this subject.

Talks and posters about every aspectof dwarf galaxies were presented. Therehave been a number of hot topics, suchas the question of dark matter in theJocal dwarf spheroidals, the big holes inthe H I component of dwarf irregulars,

the possible discontinuity betweennormal and dwarf ellipticals, and starformation.

Although there was clearly an atmo­sphere of unanimity about the subject, itwas amusing to see that there is appar­ently not yet a consensus as to thedefinition of what a dwarf galaxy iso Butthere is nothing wrong with this. A phys­ical definition of the subject would implyan understanding of the physical natureof dwarf galaxies. While we are still farfrom this goal, the workshop hasbrought us a good deal closer....

B. BINGGELI, G. MEYLAN,P PRUGNIEL

36

ANNOUNCEMENTS

CNRS - OBSERVATOIRE OE HAUTE-PROVENCE and EUROPEAN SOUTHERN OBSERVATORY

4th ESOIOHP Summer School in Astrophysical ObservationsObservatoire de Haute-Provence, France, 18-29 July 1994

The rapid advances made in the area of astronomical instrumentation had the side eftect that fewer students have ready access to up­to-date observing facilities. As a contribution to reducing this imbalance in the training of young astronomers, the ESO/OHP SummerSchool ofters the opportunity to gain practical experiences under realistic conditions.

In groups of three, each guided by an experienced observer, the participants will use the equipment of the OHP to carry out a smallobserving programme with telescopes of 1.2-1.9 metre aperture (direct imaging and spectroscopy, both with a CCO detector). to reducethe data with a modern image processing system (MIDAS or IHAP), to extract relevant additional information from the astronomicalliterature, and to describe the results in a brief summary which is to be presented to the other participants at the end of the school.

The preparation of the practical work will be supplemented by aseries of 90-minute lectures which will be given by invited specialists.Foreseen subjects include: (a) Modern Telescope Layout, (b) Oetectors, (c) Optical instrument design, (d) Principals of Photometry, (e)Spectrographs and spectroscopy, (~ IR Astronomy from the ground and from space, and (g) Oata reduction techniques. A scientific talk ona frontier astronomical subject is also foreseen.

The working language at the summer school will be English. Applications are invited from graduate students working on an astronomicalPh.O. thesis at an institute in one of the ESO member countries. Application forms are available from the organizers and have to bereturned by March 31,1994. Additionally, a letter of recommendation bya senior scientist familiar with the applicant's work is required. Upto eighteen participants will be selected and have their travel and living expenses fully covered by ESO or OHP. (Reports on the previousESO/OHP Summer Schools have appeared in The Messenger: see No. 53, p. 11, No. 61, p. 8 and No. 69, p. 17).

The Organizers:

M.P. VeronObservatoire de Haute-ProvenceF-04870 Saint-Michel-I'ObservatoireFrance

Internet:SPAN:EARN/Bitnet:

MIRA@OBSHPA.OBS-HP.FROBSHPA::MIRA

J. WamplerEuropean Southern ObservatoryKarl-Schwarzschild-Str. 20-85748 GarchingGermanyJWAMPLER@ESO.ORGESO: :JWAMPLERJWAMPLER@)OGAES051

FAX: (089) 320 2362

ESO Workshop onThe Bottom of the MainSequence - And Beyond

ESO, GarehingAugust 8-10, 1994

An ESO Workshop on the objects at, and below, the bottomof the stellar main sequence will be held from August 8-10, atthe Headquarters of the European Southern Observatory,Garching, Germany.

This workshop aims to discuss recent observational andtheoretical issues related to the lowest mass stars and browndwarfs, both in the Galactic Oisk and Halo, including thefollowing topics:

• Searches for Low Mass Objects in the Oisk and Halo• Studies of Spectral Properties• Progress in Parallaxes• Searches for Li• Progress in Models• The Teff and L Scales• Future Oirections

Scientific Organizing Committee:Chris Tinney, R.F. Jameson, Rafael Rebolo, Francesca O'An­tona, Mike Bessell, Jim Liebert, France Allard, Neill Reid.

Contact Address:Chris TinneyEuropean Southern Observatory,Karl-Schwarzschild-Str. 20-85748 Garching, Germany.e-mail: ctinney(fl eso.org

ESO Ubraries On-Une CatalogueThe ESO Libraries On-line Catalogue is now publicly avail­

able. The system allows access to the Library Catalogue for allESO libraries, informs about new acquisitions, and enableslibrary users to view their checkouts.

Users from within ESO reach the system via the riogin com­mand: riogin -I library ac4 (for users in Garching) or riogin -I Islibac4 (for users in Chile). From outside ESO, use the telnetaddress libhost.hq.eso.org, login: library (defaults will refer toMain Library in Garching) or Islib (defaults refer to La SillaLibrary).

Two user guides are available: "The ESO Libraries On-lineCatalogue in a Nutshell" and "The ESO User Guide to the On­line Catalogue". Both are available from the ESO Library inGarching (esolib Cl eso.org).

Further information about the system will be given in aforthcoming issue of the Messenger.

New ESO Publications(September-November 1993)

The SEST Handbook (ESO Operating Manual No. 19 -August 1993).

Annual Report 1992.

Scientific Preprints

939. A. Renzini: Searching for Type 1a Supernova Progenitors. Toappear in Supernovae and Supernova Remnants, lAU Coll. 154,ed. R. McCray (Cambridge University Press).

37

940. S. Savaglio et al.: The Metal Systems in QOOOO-2619 at HighResolution. Astronomy and Astrophysics.

941. L. Wisotzki et al.: The New Double QSO HE 1104-1805: Gravi­tational Lens with Microlensing or Binary Quasar? Astronomyand Astrophysics.

942. H.W. Duerbeck and EX Grebel: Recovery of the Classical NovaAR Cir. M.N.RAS.

943. J.C. Cuillandre et al.: "Va-et-Vient" Spectroscopy: a New Modefor Faint Object CCD Spectroscopy with Very Large Telescopes.Astronomy and Astrophysics.

944. E. Krügel and R. Siebenmorgen: The Transfer of Radiation inGalactic Nuclei - Dusty Hot Spots in the Star Burst Galaxy M82.Astronomy and Astrophysics.

945. R. Siebenmorgen and R.R. Peletier: Search for the 1.67 ~lm PAHEmission Band: More Upper Limits. Astronomy and Astro­physics.

946. A. Cimatti: Stellar and Scattered Light in a Radio Galaxy at z =2.63. The Astrophysical Journal.S. di Serego Alighieri and A. Cimatti: Misdirected Quasars inDistant Radio Galaxies. Paper presented at the lAU Symp. 159on "AGN across the electromagnetic spectrum", held inGeneva, August-September 1993.

947. AA Zijlstra and R. Siebenmorgen: The Past and PresentInfrared Spectrum of BD+3003639. Paper presented at theworkshop "Planetary Nebula Nuclei: Models and Observations",Bachotek, 31 August-2 September 1993.

948. O. von der Lühe: Speckle Imaging of Solar Small Scale Struc­ture. 11. Study of Small Scale Structure in Active Regions.Astronomy and Astrophysics.

949. T.R. Bedding and A.A. Zijlstra: Angular Diameters of CompactPlanetary Nebula. Astronomy and Astrophysics.

950. L. Pasquini and H. Lindgren: Chromospheric Activity in Pop 11Binaries. Astronomy and Astrophysics.

951. B. Pettersson and Bo Reipurth: Young Stars Associated with theVela Molecular Ridge: I. VMR Clouds C and 0, Collinder 197 andVela R2. Astronomy and Astrophysics.

952. S. Refsdal and J. Surdej: Gravitational Lenses. Accepted forpublication in Reports on Progress in Physics.

953. S. Benetti et al.: The Late Evolution of the Type 11 SN 1990 E.Astronomy and Astrophysics.

954. L.M. Buson et al.: The Distribution of lonized Gas in Early-TypeGalaxies. Astronomy and Astrophysics.

955. E. Bica, D. Alloin and H.R. Schmitt: Integrated Spectral Proper­ties of Star Clusters in the Near Ultraviolet. Astronomy andAstrophysics.

956. G.M. Stirpe et al.: Steps Toward Determination of the Size andStructure of the Broad-Line Region in Active Galactic Nuclei. VI.Variability of NGC 3783 from Ground-Based Data. TheAstrophysical Journal.

957. M. Della Valle and M. Livio: On the Nova Rate in the Galaxy.Astronomy and Astrophysics.

958. E.K. Grebel et al.: Be Stars in Young Clusters in the MagellanicClouds. D.J. Bomans and E.K. Grebel: Blue and Red Super­giants and the Age Structure of the NGC 330 Region. Papersaccepted for publication in Space Seience Reviews.

959. H. Van Winckel et al.: V417 Cen: A Yellow Symbiotic System in aResolved Nebula. Astronomy and Astrophysics.

960. M.C. Festou, H. Rickman and R.M. West: Comets. Astronomy &Astrophysics Reviews.

Teehnieal Preprints

56. A.F.M. Moorwood: IR Array Instruments for the ESO VLT. Toappear in Infrared Astronomy with Arrays: The Next Generation,ed. I. McLean, Kluwer: Dordrecht.

38

57. N. Hubin, J.L. Beuzit, E. Gendron, L. Demailly: ADONIS - a User­Friendly Adaptive Optics System for the ESO 3.6-m Telescope.To be published in the Proc. ICO-16 Satellite Conf. on "Active andAdaptive Optics", Garehing, August 2-5, 1993.

58. M. Cullum: Detectors. Contribution to the Commission 9 reportfor the lAU Transactions XX11 A.

59. G. Rousset et al.: The COME-ON-PLUS Adaptive Optics System:Results and Performance. To be published in the Proc. ICO-16Satellite Conf. on "Active and Adaptive Optics", Garehing, August2-5, 1993.

60. J.M. Beckers: Imaging with Array Detectors Using DifferentialDetection. Submitted for publication to Experimental Astronomy.

61. G. Filippi: Software Engineering for ESO's VLT Projeet. Paperpresented at the International Conference on Accelerator andLarge Experimental Physics Control Systems (ICALEPCS '93),held in Berlin, Germany, October 18-22, 1993.

Proceedings of the5th ESO/ST-ECF Data Analysis

Workshop Available(ESO Conference and Workshop Proceedings No. 47)

The proceedings of this workshop have now been published.The 230-p. volume, edited by P. J. Grosbol and R. C. E. de Ruijs­scher, may be obtained at a price of DM 30.- (including packingand surface maiI). Payments have to be made to the ESO bankaccount 2102002 with Commerzbank München or by cheque,addressed to the attention of

ESO, Financial ServicesKarl-Schwarzschild-Str.20-85748 Garehing b. München, Germany

STAFF MOVEMENTSArrivals

Europe

CHAVAN, Alberto (I). Engineer (Software)FERRAND, Didier (F), Engineer/PhysicistLEIBUNDGUT, Bruno (CH), AstronomerMINNITI, Dante (RA), Fellow

Departures

Europe

BOSSE, Nathalie (F), SecretaryCAROLLO, Marcella (I). StudentKJELDSEN, Hans (DK), FellowKOLB, Manfred (0), StudentWOLOHAN, Deirdre (IRL). Administrative Clerk (Personnei)ZHU, Nenghong (RC), Associate

Chile

CAPPELLARO, Enrico (I), AssociateDELLA VALLE, Massimo (I), Fellow

MESSENGER INDEX 1992-1993 (Nos. 67-74)

SUBJECT INDEX

Solar System

R.M West: Minor Planet Diseovered at ESOis Named "Chile" 67, 33

R.M West: Another Chiron-type Objeet67,34

0. Hainaut, A Smette, R.M West: HalleyBack to Normal 68, 36

L.D. Schmadel: The ESO Minor Planet Sky69, 32

H. Böhnhardt, K. Jockers, N. Kiselev, G.Schwehm, N. Thomas: Comet P/Grigg­Skjellerup Observations at ESO La SillaDuring the Giotto Eneounter Period 69, 38

R.M West, H.-H. Heyer, J Quebatte: A MinorPlanet with a Tail! 69, 40

R.M West and 0. Hainaut: New Objeet at theEdge of the Solar System 70, 33

M Di Martino, M Gonano-Beurer, S. Mottola,G. Neukum: Physieal Study of Trojan As­teroids: a Photometrie Survey 71, 10

O. Hainaut and R.M West: Another Trans­Plutonian Minor Planet: 1993 FW 72, 17

Stars

M Niehues, A Bruch, H. W. Dürbeck: Obser­vations of the Symbiotie Star BD -21 0 3873within the Long-Term Photometry of Vari­ables Programme 67,38

L.o. Loden: A Serutiny of HD 62623 and HD96446 68, 26

E Poretti and L. Mantegazza: Doing Re­search with Small Teleseopes: FrequeneyAnalysis of Multiperiodie 0 Seuti Stars68,33

S. Ortolani, E Bica, B. Barbuy: An Intermedi­ate Age Component in a Bulge Field 68, 54

E Oblak et al.: Profile of a Key Pro-gramme: CCD and Conventional Photome­try of Components 01 Visual Binaries 69, 14

A Vidal-Madjar et al.: Observation of the Cen­tral Part of the ßPictoris Disk with an Anti­Blooming CCD 69, 45

N.S. van der Bliek et al.: Profile of an ESOKey Programme: Standard Stars for the In­frared Spaee Observatory, ISO 70, 28

H. Hensberge, J Manfroid, C. Sterken:Long-Term Stability in Classieal Photome­try 70, 35

G. Cayrel de Strobel: The Contribution of De­tailed Analyses of F, G, and K Stars to theKnowledge of the Stellar Populations of theGalaetie Disk 70, 37

B. Barbuy. J Gregorio-Hetem, B. V. Castilho:A Study of T Tauri Stars and Li-Rieh GiantStar Candidates 70, 43

MD. Guamieri et al.: IR Stellar Photometry inGlobular Clusters Using IRAC2 70,44

J Storm and A Moneti: Distanees to Ex­tragalaetie RR Lyrae Stars Using IRAC270, 50

J. Bouvier: Rotation of T Tauri Stars fromMulti-Site Photometrie Monitoring 71, 21

AM Lagrange, J Bouvier, P Corporon: TYCrA: a Pre-Main-Sequenee Binary 71, 24

G. Testor and H. Schild: Woll-Rayet Stars Be­yond 1 Mpe: Why We Want to Find T~em

and How to Do It 72, 31C. Alard, A Terzan, J Guibert: Light Curves of

Miras Towards the Galaetie Centre 73, 31C.G. Tinney: CCD Astrometry 74,16B. Wolf et al.: High-Resolution Speetroseopy

at the ESO 50-em Teleseope: Speetro­seopie Monitoring 01 Galaetie LuminousBlue Variables 74, 19

P Dubath et al.: Probing the Kinematies inthe Core 01 the Globular Cluster M15 withEMMI at the NTT 74, 23

Interstellar Medium

M Lemoine, R. Ferlet, C. Emerich, A Vidal­Madjar, M Dennefeld: The Importanee ofLithium 67, 40

E Giallongo et al.: Ouasar Absorption Spee­tra: The Physieal State 01 the IntergalaetieMedium at High Redshifts 69, 52

E Palazzi, MR. Attolini, N. Mandolesi, PCrane: Probing Beyond COBE in the In­terstellar Medium 69, 59

x.-w. Liu and J Danziger: Atomie Processesand Exeitation in Planetary Nebulae 71, 25

JR. Walsh and J Meaburn: Imaging the Glob­ules in the Core of the Helix Nebula (NGC7293) 73,35

Novae, Supernovae,Supernova Remnants

M Della Valle: Nova Museae 1991: One YearLater 67,35

L. Wang and M Rosa: Light Eehoes fromSN 1987 A 67,37

PA Caraveo, G.F. Bignami, S. Mereghetti, MMombelli: On the Optieal Counterpart 01PSR 0540-693 68, 30

I.J Danziger and P Bouchet: Radioaetive iso­topes 01 Cobalt in SN 1987 A 68, 53

A Bianchini, M Della Valle, H. W. Dürbeck, MOrio: A Very Low Resolution SpeetrometrieNova Survey 69, 42

H. W. Dürbeck, R. Dümmler, W. C. Seifter,EM Leibowitz, MM Shara: The Reeur­rent Nova U Seo - a Touchstone of NovaTheories 71, 19

Supernova Diseovered at ESO 67, 59

Galaxies

R. West: The Andromeda Galaxy 67, 15G. Vettolani et al.: Profile of a Key Pro­

gramme: A Galaxy Redshift Survey in theSouth Galaetie Pole Region 67,26

D. Proust and H. Quintana: Speetroseopie Ob­servations in the Cluster 01 Galaxies Abell151 68,36

M Ramella and M Nonino: The Giant Are inEMSS2137-23 69,11

G. Soucai/: Speetroseopy of Ares and Arcletsin Rieh Clusters of Galaxies 69, 48

A Buzzoni, M Longhetti, E Molinari, G. Chin­carini: The Galaxy Population in DistantClusters 69, 55

R.F. Peletier and JH. Knapen: LookingThrough the Dust - the Edge-On GalaxyNGC 7814 in the Near Infrared 70,57

L. Infante et al.: Dark Matter in CL0017(z=0.272) 70, 61

S. Barde/li et al.: Study of the Shapley Super­cluster 71, 34

D. Block, P Grosbßl, A Moneti, P Patsis:IRAC2 Observations of the Spiral GalaxyNGC 2997 71,41

M Naumann, R. Ungruhe, W.C. Seitter: TheESO Red Sky Survey - a Tool for Galaetieand Cosmologieal Studies 71, 46

P Fouque, D. Proust, H. Quintana, R.Ramirez: Dynamies of the Pavo-Indus andGrus Clouds of Galaxies 72, 42

W. W. Zei/inger, P Mßller, M Stiavelli: Probingthe Properties 01 Elliptieal Galaxy Cores:Analysis of High Angular Resolution Obser­vational Data 73, 28

M Kissler et al.: NGC 4636 - a Rieh Glob­ular Cluster System in aNormal ElliptiealGalaxy 73, 32

Magellanic Clouds

L. Wang: A Honeyeomb in the Large Magel­lanie Cloud 69, 34

M Azzopardi: Two New Catalogues of SmallMagellanie Cloud Members Coming Soon71,29

Quasars, Seyfertand Radio Galaxies

P Magain, J Surdej, C. Vanderriest, B.Pirenne, D. Hutsemekers: The New Grav­itational Lens Candidate 0 1028+1 011 andthe Importanee of High Ouality Data 67, 30

G. Mi/ey et al.: Distant Radio Galaxies 68, 12Chr. de Vegt: Astrometry with ESO Tele­

seopes. A Contribution to the Construetionof the New Extragalaetie Referenee Frame69,28

B. Koribalski and R.-J. Dettmar: High-Resolution Imaging with the NTT: The Star­burst Galaxy NGC 1808 71, 37

D. Reimers, L. Wisotzki, Th. Köhler: NewBright Double Ouasar Diseovered - Gravi­tational Lens or Physieal Binary? 72, 39

MR.S. Hawkins et al.: A New Ouasar Pair:02126-4350 and 02126-4346 74,27

X-Rayand Gamma-Ray Sources

G.F. Bignami, PA Caraveol, S. Mereghetti:SUSI Discovers Proper Motion and Identi­fies Geminga 70, 30

I.F. Mirabel: The Great Annihilator in the Cen­tral Region 01 the Galaxy 70,51

39

N. Lund: Keeping an Eye on the X-Ray Sky70,55

First Optical Identification of an ExtragalacticPulsar 72, 27

Instrumentation,Data Processing, etc.

H. van der Laan: The VLT Progresses as itsProgramme Management is Adapted 67, 2

M Tarenghi: VLT News 67,2H. van der Laan: Contracts Signed for Two

VLT Instruments: FORS and CONICA 67,15

R. Lenzen and 0. von der Lühe: CoudaNear Infrared Camera Instrument ContractSigned 67, 17

I. Appenzeller and G. Rupprechl: FORS - theFocal Reducer for the VLT 67, 18

M Faucherre and B. Koehler: Delay Linesof the VLT Interferometer: Current Status67, 21

A. Moorwood and G. Finger: IRAC2 - ESO'sNew Large Format Infrared Array Camera67, 21

F. Malbel: A Coronagraph for COME-ON, theAdaptive Optics VLT Prototype 67,46

N. Hubin and E Gendron: News from the VLTAdaptive Optics Prototype Project: A NewPhoton Counting Wavefront Sensor Chan­nel for COME ON PLUS 67, 49

L. Pasquini, G. Rupprechl, A. Gilliotte, J.-L. U­zon: A New Cross Disperser for CASPEC67, 50

A. Giliotte, J. Melnick, J. Mendez: News AboutImaging Filters 67,51

ESO Image Processing Group: MIDAS Memo67, 51

P Oierickx and W. Ansorge: Mirror Containerand VLT 8.2-m Dummy Mirror Arrive at RE­OSC 68,6

JM Beckers: Introducing the First InstrumentScience Teams 68, 8

R.M Wesl: New R.E.O.S.C. Polishing Facilityfor Giant Mirrors Inaugurated 68, 10

H.-J. Bräuer and B. Fuhrmann: The Son­neberg Plate Archive 68, 24

A. Moorwood el al.: First Images with IRAC268, 42

N. Whyborn, L.-A. Nyman, W. Wild, G. Oel­gado: 350 GHz SIS Receiver Installed atSEST 68,45

A. Gilliotte: Fine Telescope Image Analysis atLa Silla 68, 46

A. Gilliotte, P Giordano, A. Torrejon: The DustWar 68,46

G. Richter, G. Longo, H. Lorenz, S. Zaggia:Adaptive Filtering of Long Slit Spectra ofExtended Objects 68 48

E Poretti: The Determination of the Dead­Time Constant in Photoelectric Photometry68, 52

A. Balestra et al.: NTT Remote Observingfrom Italy 69, 1

J.M Beckers: A Fourth VLT Instrument Sci­ence Team 69, 5

M Franchini et al.: "Remote" Science with theNTT from Italy. Preliminary Scientific Re­sults 69,6

A. Moorwood et al.: IRAC2 at the 2.2-m Tele­scope 69,61

L. Pasquini, H. W. Oürbeck, S. Deiries, S.O'Odorico, R. Reiss: A New 2048x2048CCD for the CES Long Camera 69, 68

L. Gonzalez, O. Hofstadt, R. Tighe: New CCDCryostat for EFOSC2 69, 70

40

A. Moorwood: ISAAC -Infrared Spectrometerand Array Camera for the VLT 70, 10

H. Oekker and S. O'Odorico: UVES, the UV­Visual Echelle Spectrograph for the VLT70, 13

L. Zago: The Choice of the Telescope Enclo­sures for the VLT 70, 17

L. Zago: The VLT Enclosure from the User'sStandpoint 70, 19

R. Gredel and U. Weilenmann: New Featuresof IRSPEC 70, 62

H.u. Käufl et al.: TIMMI at the 3.6-m Tele­scope 70,67

F. Murtagh: Astronomical Data Handling:Windows of Opportunity and of Challenge70, 71

R. Hook: ESO Computer Networking 70, 76P Grosbel: Electronic Network Access to ESO

70, 79ESO Image Processing Group: The New MI­

DAS Release; 92NOV 70, 80EJ Wampler: FFT Removal of Pattern Noise

in CCD Images 70, 82E Gendron and N. Hubin: Adaptive Optics on

the 3.6-m Telescope: Latest News! 70, 84R. de Ruijsscher: Where is MIDAS Available?

70, 85R.M Wes I: ESO, CNRS and MPG Sign

Agreement on Enhancement of the VLT in­terferometer 71, 1

M Quattri: The VLT Main Structure 71, 2P Oierickx: Manufacturing of the 8.2-m Zero­

dur Blanks for the VLT Primary Mirror 71, 5Bo Reipurth: Availability of Schmidt Emulsions

71,10K.-H. Oünsing et al.: Prototype of the FORS

Multiple-Object Spectroscopy Unit UnderTest 71,43

L. Vigroux el al.: L1TE: the Large Imaging Tele­scope 71,44

N. Hubin, G. Rousset, J.L. Beuzit, C. Boyer,J C. Richard: First Technical Run of theCOME-ON-PLUS at the ESO 3.6-m Tele­scope 71,50

J.L. Beuzit and N. Hubin: ADONIS - a UserFriendly Adaptive Optics System for the3.6-m Telescope 71, 52

HE Schwarz and TMC. Abbott: Nonlinear­ity Problems with Generation 3 CCD Con­trollers 71, 53

L. Pasquini and A. Gilliotte: CASPEC Im­provements 71, 54

P Kjaergaard: First Images from DEFOSC71,57

TA. Birulya, O.K. Mikhailov, P V. Sheglov:A New Fine-Grain Photographic Emulsion71,57

E Poretti: Correction "On the Dead-Time Con­stant in Photon-Counting Systems" 71, 58

M Tarenghi: The VLT: Important ContractsConcluded 72, 4

O. Baade et al.: Remote Observing with theNTT and EMMIISUSI: a First Assessment72,13

A. Ferrari et al.: CCD Photometric Standardsfor the Southern Sky: a Status Report72,18

E Aubourg et al.: The EROS Search for DarkHalo Objects 72, 20

M Redfern et al.: TRIFFID Imaging of 47 Tucon the NTT 72, 29

V. de Lapparent et al.: Mapping the Large­Scale Structure with the ESO Multi-SlitSpectrographs 72, 34

H.U. KäufI: Phase-A Study Launched for the10/20 J.Lm CameralSpectrometer for ESO'sVLT 72,44

F. Murtagh and H.-M Adorf: AstronomicalLiterature Publicly Accessible On-Line: aShort Status Report 72, 45

R. Müller, H. Höness, J Espiard, J Paseri, POierickx: The 8.2-m Primary Mirrors of theVLT 73,1

H.U. Käufl: Ground-Based Astronomy in the10 and 20 J.Lm Atmospheric Windows atESO - Scientific Potential at Present andin the Future 73, 8

EGosset and P Magain: On the Linearity ofESO CCD #9 at CAT + CES 73,13

TMC. Abbott and P Sinclaire: CCD Linearityat La Silla - a Status Report 73, 17

F. Murtagh, W. W. Zeilinger, J -L. Starck, H.Böhnhardt: Detection of Faint ExtendedStructures by Multiresolution Wavelet Anal­ysis 73,37

MA. Albrecht and A. Heck: StarGates andStarWords - an On-Line Yellow Pages Di­rectory for Astronomy 73, 39

M Tarenghi: VLT News from the VLT Division74, 1

TR. Bedding et al.: First Light from the NTTInterferometer 74, 2

H. Oahlmann et al.: Optical Gyro EncoderTested on the NTT 74, 5

A. Moorwood and G. Finger: Infrared As­tronomy with Arrays: the Next Generation74, 6

O. Iwert: Current CCD Projects and Their Re­lation to the VLT Instruments 74,7

ESO Image Processing Group: The 93NOVRelease of ESO-MIDAS 74,33

C. Guirao: An ESO-MIDAS Implementationfor PC/Linux 74, 34

O. Hofstadt et al.: DDS/DAT Tape Cartridgesas New ESO Tape Standard 74, 35

First 8.6-m Glassy Meniscus Blank for the VLT67, 1

Seeing, AtmosphericEffects and VLT Site

F. Bourlon: A Geological Description of CerroParanal or Another Insight Into the "PerfectSite for Astronomy" 67, 4

MA. Fluks and PS. TM: On Flux Calibrationof Spectra 67, 42

M Sarazin: PARSCA 92: The Paranal SeeingCampaign 68, 9

H.-G. Grothues and J Gochermann: The In­fluence of the Pinatubo Eruption on the At­mospheric Extinction at La Silla 68, 43

M Sarazin and J Navarrele: Seeing atParanal: Mapping the VLT Observatory71,7

G. Mateshvili and Y Mateshvili: Dust in theEarth's Atmosphere Before and After thePassage of Halley's Comet (1984-1987)71, 14

A Paranal Portfolio 67, 12Paranal (October 1992) 70, 6

Science with the VLT

J Lequeux: The Magellanic Clouds and theVLT 73, 19

M Sliavelli: Nuclei of Non-Active Galaxieswith the VLT 73, 21

R. Ferlet: From Planets to the Big Bang withHigh-Resolution Spectroscopy at the VLT73, 25

R. Fosbury et al.: The Limits of Faint-ObjectPolarimetry 74,11

Organizational MaUers

H. van der Laan: The Squeeze is on the LaSilla Observatory 69, 12

H. van der Laan: The Idea of the EuropeanSouthern Observatory 70, 3

G. Bachmann and M Tarenghi: Develop­ments in ESO/Chile 70, 5

R. Giacconi: Current ESO Activities 72, 1R.M West: Relations Between the Republic

01 Chile and ESO 72, 3

Riccardo Giacconi - ESO's Next Director Gen­eral 68, 1

Supplementary and Modifying Agreement Re­garding the 1963 Convention Between TheGovernment of Chile and The EuropeanSouthern Observatory (ESO) 72, 4

Other Topics

po. Lindblad and A. Blaauw: Gösta W. Funke1906-1991 67,24

C. Madsen: ESO at EXPO '92 67,48E. Oavoust: Jean-Luc Nieto (1950-1992)

67, 48RM West: Things that Pass in the Sky 67,52E. Fosbury, A. Turtle, M Black: Astronomical

Light Pollution by Artificial Satellites 67,53O. Hainaut: Unidentified Object Over Chile

67, 56A. Smelte and 0. Hainaut: A Near Miss?

67, 57J. Lequeux: The Future of Astronomy Publi­

cations: Electronic Publishing? 67,58O.A. Verner: Astronomy Acknowledgements

Index 1991 67,61OB. Herrmann: On the Life Expectancy 01

Astronomers 67,62M-H. Ulrich: Bigger Telescopes and Better

Instrumentation: Report on the 1992 ESOConlerence 68, 1

R.M West: European Planetarians Meet atESO Headquarters 68, 15

P Bouchet, A. Cabillic, C. Madsen: ESO Ex­hibitions in Chile - a Tremendous Success68,18

RM West: The Youngest Visitors Yet 68, 20RM West: A Most Impressive Astronomy Ex­

hibition 68, 21O. AIIoin and T. Le Bertre: Astronomical Ob­

servations in 2001 68, 22H. Zodet: A Panorama 01 La Silla 68, 28R.M West: Russian Comets and American

Rockets 68, 39R. Rast: Close Encounters with lee Balls of a

Second Kind 68, 40I. Ferrin: On the Nature of the Smette-Hainaut

Object 68, 40R. Rast and N. Johnson: Unidentified Object

Over Chile Identified 68, 41H. Böhnhardt: On the "Unidentilied Object

Over Chile" 68, 42M Veron and O. Baade: The 3rd ESOIOHP

Summer School: Proven9al Summer, HardWork and Warm Hospitality 69, 17

G. Alcaino and W. Liller: The Instituto IsaacNewton: A Highly Productive ESO-ChileConnection 69, 21

The ESO Aficionados: The Other Face of LaSilla 69,25

S. O'Odorico: Alive and Kicking into the 90's69, 27

H. van der Laan: Jan Hendrick Oort (1900­1992) - Looking Ahead in Wonder 70, 1

R.M West: ESO to Help Central and EasternEuropean Astronomers 70, 8

R.M West: ESA Astronaut Claude NicollierVisits ESO 70, 9

U. Michold: Something is Going On in theESO-Libraries 70, 21

C. Madsen: "Exploring the Universe" from theDesert Gate 70, 24

H. Zodet: ESO in Milan. Some Notes on theAssembly 01 an ESO Exhibition 70, 26

P Lena: Professor Lodewijk Woltjer Electedto the French Academy 01 Sciences 70,27

A. Smelte: Fire at the 1-m Telescope! 70, 70H. Barwig and K.H. Mantel: Acknowledge­

ment 70,70M Creze, A. Heck, F. Murtagh: Report on

ALD-II, Astronomy Irom Large Databases70, 80

R.M West: The End of the Earth? 70, 87

R.M West: Riccardo Giacconi Receives HighNASA Honour 71, 3

A. Blaauw: The ESO Historical Archives(EHA). Inventory per December 1992 71,9

R.M West: The ESO C&EE Programme Be­gins 71,9

DA Verner: Astronomy AcknowledgementIndex 1992 71,59

P Aniol: Amateur Astronomy with CCDs71,60

K. Kjär: Development 01 ESO Publications71,61

R.M West: ESO C&EE Programme: aProgress Report 72, 6

R.M West: The ESO-Portugal Cooperation72, 8

RM West: Change 01 Editor 72, 10C. Madsen: ESO Exhibition in Florence

72,10J Andersen: Ray Tracing Twenty Years at

ESO 72,12C. Madsen: ESO at CNRS Plenary Meeting

72,12H.-H. Heyer: A Two-Colour Composite 01 IC

1396 72, 16B. Altieri: "EI C6ndor Loco" Tests the La Silla

Winds 72,29R.M. West: What Is This? 72, 40M-H. Ulrich: A Message lrom the New Editor

73, 1L. Vigroux: VLT Working Group lor Scientilic

Priorities - Status 01 the Work 74, 28J Andersen: Scientilic Priorities lor La Silla

Operations 74, 29J Breysacher and J Andersen: Proposal

Statistics 74, 30B. Binggeli et al.: ESOIOHP Workshop on

Dwarf Galaxies 74, 36

H.-W. Marck 1914-1992 68,23Sporty ESO 69, 25More 1910 Halley Memorabilia 71, 17ESO Visitor Programme at Garehing 72, 7"Future Astronomers 01 Europe" - ESO's Con-

tribution to the European Week lor Scien­tilic Culture 72, 9

"Astronomieal" Organ Concert in the La Ser­ena Cathedral 72, 11

AUTHOR INDEX

A

T.MC. Abbolt and P Sinclaire: CCD Linearityat La Silla - a Status Report 73, 17

C. Alard, A. Terzan, J Guibert: Light Curves 01Miras Towards the Galactic Centre 73, 31

M.A. Albrecht and A. Heck: StarGates andStarWords - an On-Line Yellow Pages Di­rectory for Astronomy 73, 39

G. Alcaino and W. Liller: The Institute IsaacNewton: A Highly Productive ESO-ChileConnection 69, 21

O. Alloin and T. Le Bertre: Astronomical Ob­servations in 2001 68, 22

B. Altieri: "EI C6ndor Loco" Tests the La SillaWinds 72,29

J Andersen: Ray Tracing Twenty Years atESO 72, 12

J Andersen: Scientilic Priorities lor La SillaOperations 74, 29

P Aniol: Amateur Astronomy with CCDs71,60

I. Appenzeller and G. Rupprecht: FORS - theFocal Reducer for the VLT 67, 18

E. Aubourg et al.: The EROS Search for DarkHalo Objects 72, 20

M Azzopardi: Two New Catalogues of SmallMagellanic Cloud Members Coming Soon71,29

B

O. Baade et al.: Remote Observing with theND and EMMI/SUSI: a First Assessment72, 13

G. Bachmann and M Tarenghi: Develop­ments in ESO/Chiie 70, 5

A. Balestra et al.: ND Remote ObservingIrom Italy 69, 1

B. Barbuy, J Gregorio-Hetem, B. V Castilho:A Study 01 T Tauri Stars and Li-Rich GiantStar Candidates 70, 43

S. Bardelli et al.: Study 01 the Shapley Super­cluster 71, 34

H. Barwig and K.H. Mantel: Acknowledge­ment 70,70

T.R. Bedding et al.: First Light Irom the NDInterferometer 74, 2

A. Bianchini, M Oella Valle, H. W. Oürbeck, M.Orio: A Very Low Resolution SpectrometricNova Survey 69, 42

G.F. Bignami, PA. Caraveol, S. Mereghelti:SUSI Discovers Proper Motion and Identi­fies Geminga 70, 30

JM Beckers: Introducing the First InstrumentScience Teams 68, 8

JM Beckers: A Fourth VLT Instrument Sci­ence Team 69, 5

O. Block, P Grosbel, A. Moneti, P Patsis:

41

IRAC2 Observations 01 the Spiral GalaxyNGC 2997 71,41

J.L. Beuzit and N. Hubin: ADONIS - a UserFriendly Adaptive Opties System lor the3.6-m Teleseope 71, 52

B. Binggeli et al.: ESOIOHP Workshop onDwarf Galaxies 74, 36

T.A Birulya, O.K. Mikhai/ov, P V. Sheglov:A New Fine-Grain Photographie Emulsion71,57

A Blaauw: The ESO Historieal Archives(EHA). Inventory per Deeember 1992 71, 9

H Böhnhardt: On the "Unidentilied ObjeetOver Chile" 68, 42

H Böhnhardt, K Jockers, N. Kiselev, G.Schwehm, N. Thomas: Comet P/Grigg­Skjellerup Observations at ESO La SillaDuring the Giotto Eneounter Period 69, 38

P Bouchet, A Gabillic, G. Madsen: ESO Ex­hibitions in Chile - a Tremendous Sueeess68, 18

F. Bourlon: A Geologieal Deseription 01 CerroParanal or Another Insight Into the "PerfeetSite lor Astronomy" 67, 4

J. Bouvier: Rotation 01 T Tauri Stars IromMulti-Site Photometrie Monitoring 71, 21

H -J. Bräuer and B. Fuhrmann: The Son­neberg Plate Archive 68, 24

J. Breysacher and J. Andersen: ProposalStatisties 74, 30

A Buzzoni, M Longhetti, E Molinari, G. Ghin­carini: The Galaxy Population in DistantClusters 69, 55

cPA Garaveo, G.F. Bignami, S. Mereghetti, M

Mombelli: On the Optieal Counterpart 01PSR 0540-693 68, 30

G. Gayrel de Strobel: The Contribution 01 De­tailed Analyses 01 F, G, and K Stars to theKnowledge 01 the Stellar Populations 01 theGalaetie Disk 70, 37

M Greze, A Heck, F. Murtagh: Report onALD-II, Astronomy lrom Large Databases70, 80

DH. Oahlmann et al.: Optieal Gyro Encoder

Tested on the ND 74, 5I.J. Danziger and P Bouchet: Radioaetive Iso­

topes 01 Cobalt in SN 1987 A 68, 53E Oavoust: Jean-Lue Nieto (1950-1992)

67,48H. Oekker and S. O'Odorico: UVES, the UV­

Visual Eehelle Speetrograph lor the VLT70, 13

V. de Lapparent et al.: Mapping the Large­Seale Strueture with the ESO Multi-SlitSpeetrographs 72, 34

M Oella Valle: Nova Museae 1991: One YearLater 67,35

R. de Ruijsscher: Where is MIDAS Available?70, 85

Ghr. de Vegl: Astrometry with ESO Tele­seopes. A Contribution to the Construetion01 the New Extragalaetie Relerenee Frame69, 28

P Oierickx and W. Ansorge: Mirror Containerand VLT 8.2-m Dummy Mirror Arrive at RE­OSC 68,6

P Oierickx: Manulacturing of the 8.2-m Zero­dur Blanks for the VLT Primary Mirror 71,5

M Oi Martino, M Gonano-Beurer, S. Mottola,G. Neukum: Physieal Study 01 Trojan As­teroids: a Photometrie Survey 71, 10

42

S. O'Odorico: Alive and Kicking into the 90's69, 27

P Oubalh el al.: Probing the Kinematics inthe Core of the Globular Cluster M15 withEMMI at the ND 74,23

K-H. Oünsing el al.: Prototype of the FORSMultiple-Objeet Speetroseopy Unit UnderTest 71,43

H. W. Oürbeck, R. Oümmler, w.G. Seitter,EM Leibowitz, MM Shara: The Reeur­rent Nova U Seo - a Touchstone of NovaTheories 71, 19

E

ESO Image Processing Group: MIDAS Memo67, 51

ESO Image Processing Group: The New MI­DAS Release; 92NOV 70, 80

ESO Image Processing Group: The 93NOVRelease of ESO-MIDAS 74, 33

F

M Faucherre and B. Koehler: Delay Linesof the VLT Interferometer: Current Status67, 21

R. Ferlel: From Planets to the Big Bang withHigh-Resolution Speetroseopy at the VLT73, 25

A Ferrari el al.: CCD Photometrie Standardslor the Southern Sky: a Status Report72,18

I. Ferrin: On the Nature of the Smette-HainautObjeet 68, 40

MA Fluks and PS. TM: On Flux Calibration01 Speetra 67, 42

E Fosbury, A Turtle, M Black: AstronomiealLight Pollution by Artificial Satellites 67,53

R. Fosbury el al.: The Limits of Faint-ObjeetPolarimetry 74, 11

P Fouque, O. Proust, H Quinlana, R.Ramirez: Dynamies of the Pavo-Indus andGrus Clouds of Galaxies 72, 42

M Franchini el al.: "Remote" Seienee with theND lrom Italy. Preliminary Seientifie Re­sults 69,6

G

E Gendron and N. Hubin: Adaptive Opties onthe 3.6-m Teleseope: Latest News! 70, 84

R. Giacconi: Current ESO Aetivities 72, 1E Giallongo el al.: Quasar Absorption Spee­

tra: The Physieal State of the IntergalaetieMedium at High Redshifts 69, 52

A Gi/iotte, J. Melnick, J. Mendez: News AboutImaging Filters 67, 51

A Gilliotte: Fine Teleseope Image Analysis atLa Silla 68, 46

A Gilliotte, P Giordano, A Torrejon: The DustWar 68,46

L. Gonzalez, O. Hofsladl, R. Tighe: New CCDCryostat for EFOSC2 69, 70

EGossei and P Magain: On the Linearity ofESO CCD #9 at CAT + CES 73,13

R. Gredel and U. Wei/enmann: New Featuresof IRSPEC 70, 62

P Grosbel: Eleetronie Network Aeeess to ESO70, 79

H.-G. Grothues and J. Gochermann: The In­fJuenee of the Pinatubo Eruption on the At­mospherie Extinetion at La Silla 68, 43

MD. Guarnieri el al.: IR Stellar Photometry inGlobular Clusters Using IRAC2 70,44

G. Guirao: An ESO-MIDAS Implementationfor PC/Linux 74, 34

H0. Hainaut: Unidentified Objeet Over Chile

67, 56O. HainauI, A Smette, R.M West: Halley

Back to Normal 68, 360. Hainaut and R.M Wesl: Another Trans­

Plutonian Minor Planet: 1993 FW 72, 17MR.S. Hawkins et al.: A New Quasar Pair:

Q2126-4350 and Q2126-4346 74,27H Hensberge, J. Manfroid, G. Sierken:

Long-Term Stability in Classieal Photome­try 70,35

O.B. Herrmann: On the Life Expeetaney 01Astronomers 67,62

H-H Heyer: A Two-Colour Composite 01 JC1396 72, 16

O. Hofsladl el al.: DDS/DAT Tape Cartridgesas New ESO Tape Standard 74,35

R. Hook: ESO Computer Networking 70, 76N. Hubin and E Gendron: News from the VLT

Adaptive Opties Prototype Projeet: A NewPhoton Counting Wavefront Sensor Chan­nel for COME ON PLUS 67, 49

N. Hubin, G. Roussel, J.L. Beuzil, G. Boyer,J.G. Richard: First Teehnieal Run of theCOME-ON-PLUS at the ESO 3.6-m Tele­seope 71,50

L. Infante et al.: Dark Matter in CL0017(z=0.272) 70, 61

O. Iwert: Current CCD Projeets at ESO andTheir Relation to the VLT Instruments 74,7

K

HU. Käufl et al.: TIMMI at the 3.6-m Tele­seope 70,67

H U. KäufI: Phase-A Study Launched lor the10/20 J.Lm CameralSpeetrometer lor ESO'sVLT 72,44

H.U. Käull: Ground-Based Astronomy in the10 and 20 J.Lm Atmospherie Windows atESO - Seientilie Potential at Present andin the Future 73, 8

M Kissler el al.: NGC 4636 - a Rieh Glob­ular Cluster System in aNormal ElliptiealGalaxy 73, 32

P Kjaergaard: First Images Irom DEFOSC71,57

K. Kjär: Development 01 ESO Publieations71,61

B. Koribalski and R.-J. Oettmar: High-Resolution Imaging with the ND: The Star­burst Galaxy NGC 1808 71, 37

LAM Lagrange, J. Bouvier, P Gorporon: TY

CrA: a Pre-Main-Sequence Binary 71, 24M Lemoine, R. Ferlel, G. Emerich, A Vidal­

Madjar, M Oennefeld: The Importanee 01Lithium 67, 40

P Lena: Prolessor Lodewijk Wolljer Eleetedto the Freneh Aeademy 01 Seiences 70, 27

J. Lequeux: The Future 01 Astronomy Publi­eations: Eleetronic Publishing? 67, 58

J. Lequeux: The Magellanie Clouds and lheVLT 73,19

Po. Lindblad and A. Blaauw: Gösta W. Funke1906-1991 67, 24

x.-w. Liu and J. Danziger: Atomic Processesand Excitation in Planetary Nebulae 71, 25

L.a. Loden: A Scrutiny of HD 62623 and HD96446 68,26

M

C. Madsen: ESO at EXPO '92 67,48G. Madsen: "Exploring the Universe" from the

Desert Gate 70, 24G. Madsen: ESO Exhibition in Florence

72, 10G. Madsen: ESO at CNRS Plenary Meeting

72, 12P. Magain, J. Surdej, G. Vanderriest, B.

Pirenne, D. Hutsemekers: The New Grav­itational Lens Candidate Q 1028+1011 andthe Importance of High Quality Data 67, 30

F. Malbet: A Coronagraph for COME-ON, theAdaptive Optics VLT Prototype 67,46

G. Mateshvili and Y. Mateshvili: Dust in theEarth's Atmosphere Before and After thePassage of Halley's Comet (1984-1987)71, 14

U. Michold: Something is Going On in theESO-Libraries 70, 21

G. Mi/ey et al.: Distant Radio Galaxies 68, 12I.F. Mirabel: The Great Annihilator in the Cen­

tral Region of the Galaxy 70, 51A. Moorwood and G. Finger: IRAC2 - ESO's

New Large Format Infrared Array Camera67, 21

A. Moorwood et al.: First Images with IRAC268,42

A. Moorwood et al.: IRAC2 at the 2.2-m Tele­scope 69, 61

A. Moorwood: ISAAC - Infrared Spectrometerand Array Camera for the VLT 70, 10

A. Moorwood and G. Finger: Infrared As­tronomy with Arrays: The Next Generation74, 6

R. Müller, H. H6ness, J. Espiard, J. Paseri, P.Dierickx: The 8.2-m Primary Mirrars of theVLT 73, 1

F. Murtagh: Astronomical Data Handling:Windows of Opportunity and of Challenge70, 71

F. Murtagh and H. -M. Adorf: AstronomicalLiterature Publicly Accessible On-Line: aShort Status Report 72, 45

F. Murtagh, W. W. Zei/inger, J. -L. Starck, H.B6hnhardt: Detection of Faint ExtendedStructures by Multiresolution Wavelet Anal­ysis 73,37

N

M Niehues, A. Bruch, H. W. Dürbeck: Obser­vations of the Symbiotic Star BD -21 0 3873within the Long-Term Photometry of Vari­ables Programme 67, 38

oE. Oblak et al.: Profile of a Key Pro-

gramme: CCD and Conventional Photome­try of Components of Visual Binaries 69, 14

S. Ortolani, E. Bica, B. Barbuy: An Intermedi­ate Age Component in a Bulge Field 68, 54

p

E. Palazzi, MR. Attolini, N. Mandolesi, P.Grane: Probing Beyond COBE in the in­terstellar Medium 69, 59

L. Pasquini, G. Rupprecht, A. Gil/iotte, J. -L. U­zon: A New Cross Disperser far CASPEC67,50

L. Pasquini, H. W. Dürbeck, S. Deiries, S.D'Odorico, R. Reiss: A New 2048 x2048CCD for the CES Long Camera 69, 68

L. Pasquini and A. Gilliotte: CASPEC Im­provements 71, 54

R.F. Peletier and J.H. Knapen: LookingThrough the Dust - the Edge-On GalaxyNGC 7814 in the Near Infrared 70,57

E. Poretti and L. Mantegazza: Doing Re­search with Small Telescopes: FrequencyAnalysis of Multiperiodic 8 Scuti Stars68,33

E. Poretti: The Determination of the Dead­Time Constant in Photoelectric Photometry68, 52

E. Poretti: Correction "On the Dead-Time Con­stant in Photon-Counting Systems" 71, 58

D. Proust and H. Quintana: Spectroscopic Ob­servations in the Cluster of Galaxies Abell151 68,36

Q

M Quattri: The VLT Main Structure 71, 2

R

M Ramella and M Nonino: The Giant Arc inEMSS 2137-23 69, 11

R. Rast: Close Encounters with Ice Balls of aSecond Kind 68, 40

R. Rast and N. Johnson: Unidentified ObjectOver Chile Identified 68, 41

M Redfem et al.: TRIFFID Imaging of 47 Tucon the NTI 72, 29

D. Reimers, L. Wisotzki, Th. K6hler: NewBright Double Quasar Discovered - Gravi­tational Lens or Physical Binary? 72, 39

Bo Reipurth: Availability of Schmidt Emulsions71, 10

G. Richter, G. Longo, H. Lorenz, S. Zaggia:Adaptive Filtering of Long Slit Spectra ofExtended Objects 68 48

sM Sarazin: PARSCA 92: The Paranal Seeing

Campaign 68, 9M Sarazin and J. Navarrete: Seeing at

Paranal: Mapping the VLT Observatory71,7

L.D. Schmadel: The ESO Minor Planet Sky69, 32

HE Schwarz and T.MG. Abbott: Nonlinear­ity Problems with Generation 3 CCD Con­trollers 71, 53

A. Smette and O. Hainaut: A Near Miss?67, 57

A. Smette: Fire at the 1-m Telescope! 70, 70J. Storm and A. Moneti: Distances to Ex­

tragalactic RR Lyrae Stars Using IRAC270, 50

G. Soucai/: Spectroscopy of Arcs and Arcletsin Rich Clusters of Galaxies 69, 48

M Stiavelli: Nuclei of Non-Active Galaxieswith the VLT 73,21

T

M Tarenghi: VLT News 67,2M Tarenghi: The VLT: Important Contracts

Concluded 72, 4

M Tarenghi: VLT News from the VLT Division74, 1

G. Testor and H. Schild: Wolf-Rayet Stars Be­yond 1 Mpc: Why We Want to Find Themand How to Do It 72, 31

G.G. Tinney: CCD Astrometry 74, 16

uM -H. Ulrich: Bigger Telescopes and Better

Instrumentation: Report on the 1992 ESOConference 68, 1

M-H. Vlrich: A Message from the New Editor73,1

vN.S. van der Bliek et al.: Profile of an ESO

Key Programme: Standard Stars for the ln­frared Space Observatory, ISO 70, 28

H. van der Laan: The VLT Progresses as itsProgramme Management is Adapted 67,2

H. van der Laan: Contracts Signed for TwoVLT Instruments: FORS and CONICA 67,15

H. van der Laan: The Squeeze is on the LaSilla Observatory 69, 12

H. van der Laan: Jan Hendrick Oort (1900­1992) - Looking Ahead in Wonder 70, 1

H. van der Laan: The Idea of the EuropeanSouthern Observatory 70, 3

D.A. Verner: Astronomy AcknowledgementsIndex 1991 67,61

D.A. Verner: Astronomy AcknowledgementIndex 1992 71, 59

M Veron and D. Baade: The 3rd ESO/OHPSummer School: Provenyal Summer, HardWork and Warm Hospitality 69, 17

G. Vettolani et al.: Profile of a Key Pro­gramme: A Galaxy Redshift Survey in theSouth Galactic Pole Region 67,26

A. Vidal-Madjar et al.: Observation of the Cen­tral Part of the ß Pictoris Disk with an Anti­Blooming CCD 69, 45

L. Vigroux et al.: L1TE: the Large Imaging Tele­scope 71,44

L. Vigroux: VLT Working Group for ScientificPriorities - Status of the Wark 74, 28

wJ.R. Walsh and J. Meaburn: Imaging the Glob­

ules in the Care of the Helix Nebula (NGC7293) 73, 35

E.J. Wampler: FFT Removal of Pattern Noisein CCD Images 70, 82

L. Wang and M Rosa: Light Echoes fromSN 1987 A 67,37

L. Wang: A Honeycomb in the Large Magel­lanic Cloud 69, 34

R.M West: The Andromeda Galaxy 67,15R.M West: Minor Planet Discovered at ESO

is Named "Chile" 67,33R.M West: Another Chiron-type Object

67, 34R.M West: Things that Pass in the Sky 67, 52R.M West: New R.E.O.S.C. Polishing Facility

far Giant Mirrors Inaugurated 68, 10R.M West: European Planetarians Meet at

ESO vHeadquarters 68, 15R.M West: The Youngest Visitors Yet 68, 20R.M West: A Most Impressive Astronomy Ex­

hibition 68, 21R.M West: Russian Comets and American

Rockets 68, 39

43

ANNOUNCEMENTS

SCIENCE WITH THE VLT

OTHER ASTRONOMICAL NEWS

zL. Zago: The Choice 01 the Telescope Enclo­

sures lor the VLT 70, 17L. Zago: The VLT Enclosure lrom the User's

Standpoint 70, 19W. W. Zeilinger, P. Meiler, M. Stiavelli: Probing

the Properties 01 Elliptical Galaxy Cores:Analysis 01 High Angular Resolution Obser­vational Data 73, 28

H. Zodet: A Panorama 01 La Silla 68, 28H. Zodet: ESO in Milan. Some Notes on the

Assembly 01 an ESO Exhibition 70, 26

scopic Monitoring 01 Galactic LuminousBlue Variables 74,19

N. Whybom, L.-A. Nyman, W. Wild, G. Del­gado: 350 GHz SIS Receiver Installed atSEST 68,45

C.G. Tinney: CCD Astrometry . . . . . 16B. Wolf et al.: High-Resolution Spectroscopy at the ESO 50-cm Telescope:

Spectroscopic Monitoring of Galactic Luminous Blue Variables 19P. Dubath et al.: Probing the Kinematics in the Core of the Globular Cluster

M15 with EMMI at the NTT 23M.R.S. Hawkins et al.: A New Ouasar Pair: 02126-4350 and 02126-4346 27

REPORTS FROM OBSERVERS

R. Fosbury et al.: The Limits 01 Faint-Object Polarimetry 11

TELESCOPES AND INSTRUMENTATION

Contents

News from Council 1M. Tarenghi: VLT News from the VLT Division.............. 1T.R. Bedding et al.: First Light Irom the NTT Interferometer. . . . . . . . . .. . . . . . . . . 2H. Dahlmann et al.: Optical Gyro Encoder Tested on the NTT . . 5A. Moorwood and G. Finger: Infrared Astronomy with Arrays: the Next Gen-

eration 6O. Iwert: Current CCD Projects at ESO and Their Relation to the VLT Instru-

ments 7

R.M. West, H.-H. Heyer, J. Quebatte: A MinorPlanet with a Taill 69, 40

R.M. West: ESO to Help Central and EastemEuropean Astronomers 70, 8

R.M. West: ESA Astronaut Claude NicollierVisits ESO 70, 9

R.M. West and O. Hainaut: New Object at theEdge 01 the Solar System 70, 33

R.M. West: ESO, CNRS and MPG SignAgreement on Enhancement 01 the VLT In­terferometer 71, 1

R.M. West: The ESO C&EE Programme Be­gins 71,9

R.M. West: Relations Between the Republic01 Chile and ESO 72, 3

R.M. West: ESO C&EE Programme: a Pro­gress Report 72, 6

R.M. West: The ESO-Portugal Cooperation72, 8

R.M. West: Change 01 Editor 72,10B. Wolf et al.: High-Resolution Spectroscopy

at the ESO 50-cm Telescope: Spectro-

L. Vigroux: VLT Working Group for Scientific Priorities - Status of the Work 28J. Andersen: Working Group for Scientific Priorities for La Silla Operations 29J. Breysacher and J. Andersen: Proposal Statistics 30ESO Image Processing Group: The 93NOV Release of ESO-MIDAS 33C. Guirao: An ESO-MIDAS Implementation for PC/Linux 34D. Hofstadt et al.: DDS/DAT Tape Cartridges as New ESO Tape Standard 35B. Binggeli et al.: ESO/OHP Workshop on Dwarf Galaxies . . . . . . . . . . . . . . . . . . . . 36

MESSENGER INDEX 1992-1993 (Nos. 67-74) 39

4th ESO/OHP Summer School in Astrophysical Observations 37ESO Workshop on ''The Bottom of the Main Sequence - And Beyond" . . . . . . .. 37ESO Libraries On-Line Catalogue . . 37New ESO Publications 37Statt Movements 38

44