Supporting material for Lecture 1: Role of atmosphere in astronomical observations
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Supporting material for Lecture 1:
Role of atmosphere in astronomical observations
Definition of angular resolution
Optical, radio, X-ray telescopes
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Atmospheric absorption
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2.5m MountWilson telescope
Telescopio NazionaleGalileo(3.5m)
Hubble SpaceTelescope(2.4m)
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Resolution or minimum resolvable distance is the minimum distance between distinguishable objects in an image
Sources with angular size larger than the resolution are calledExtended, otherwise their are point-like, i.e., their angular Extent does not exceed the point spread function
The resolution of ground-based optical images is limited by theAtmospheric seeing (about 1-2 arcseconds on average).
How can one overcome the atmospheric limitation in optical?• By using adaptive optics • By using interferometry • By putting a telescope in space (HST)
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Adaptive optics use wavefront sensors to adapt a deformable mirror to variations of the local seeing
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Adaptive optics atGemini telescope
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Luminous infrared galaxy IRAS 18293-3413 (79 Mpc)
Comparison of NTT/SOFI and VLT/NACO images
Angular size of each image: 16.5” x 11.5”
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Four 8.2m telescopes
Resolution = /B
B = Baseline
With an ARRAY of telescopes I can combine the wave trains(aperture synthesis) and improve the resolution
INTERFEROMETRY
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VLTI/AMBER discovers a companion to HD 87643By image synthesis
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Comparison of ground-based opticaland HST Images of the HomunculusNebula around Eta Carinae. TheLarger axis of the nebula is about 30 arcseconds HST-WFPC2
VLT NACO
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Radiotelescopes
Natural concavities favourScreening from human-relatedRadio-interference
Resolution: ~10 arcmin
Arecibo (100m)
Parabola inMedicina, Bologna (32m)
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Radiointerferometry:Aperture synthesis
Very Large Array (New Mexico)
Croce del Nord (Medicina)
Angular resolution:~1 arcsec
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Very Long Baseline Array (VLBA)
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European VLBI Network (EVN)
Very Long Baseline Interferometry (ang. Res.: milliarcsecond)
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The VLBI SpaceObservatory Program(VSOP)
HALCA: Japanese 8m Antenna orbiting the Earth
Ang. Res: milli-to-microarcsec
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Relativistic jetOf the active galaxy Mkn501(z = 0.033)
30000 kmHalca
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X-ray telescopes: grazing incidence
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X-ray observations of Eta Carinae
Chandra XMM-Newton ASCA
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X-ray: 0.1 - 100 keV
The history of X-ray astronomy started in the 1960s:
R. Giacconi 2003:Nobel Lecture: The dawn of x-ray astronomyReviews of Modern Physics 75, 995
In 40 years the X-ray flux sensitivity has improved by 10 orders of magnitudes, comparable to the improvement in optical instruments sensitivity in the last 400 years!
First high-energy baloon experiments: about e-08 erg/s/cm2
Chandra (launched 1999): e-18 erg/s/cm2