KOALA: Kilofibre Optical AAT Lenslet Arrayastro.ft.uam.es › selgifs › uam2016 › slides ›...

KOALA: Kilofibre Optical AAT Lenslet Array

Ángel R. López-Sánchez Australian Astronomical Observatory / Macquarie University

@El_Lobo_Rayado 2nd SELGIFS School on IFS Data Analysis – Madrid – Spain – 22 November 2016

2nd SELGIFS School on IFS Data Analysis – Madrid – Spain – 22 Nov 2016 Ángel R. López-Sánchez

3.9m Anglo-Australian Telescope at Siding Spring Observatory


3.9m Anglo-Australian Telescope


KOALA, the Kilofibre Optical AAT Lenslet Array, is a wide-field, high efficiency, integral field unit (IFU) designed for use with the bench mounted AAOmega spectrograph on the 3.9m AAT.

KOALA has 1000 hexagonal lenslets arranged in a rectangular array.

KOALA: The AAT IFU instrument

The field of view is selectable:

15.3” x 28.3”, with 0.7” spatial sampling

27.4” x 50.6” with 1.25” spatial sampling

To achieve this, KOALA uses a telecentric double-lenslet array fed by interchangeable fore-optics.

https://www.aao.gov.au/science/instruments/current/koala/overview



The IFU is mounted at the f/8 Cassegrain focus and feeds the AAOmega spectrograph via a 31m fibre run.





KOALA benefits from all of the flexibility of the reconfigurable AAOmega spectrograph. The double beam spectrograph provides user selectable wavelength coverage and resolution using a series of movable, interchangeable gratings.


A set of low, medium, and high resolution gratings provide R~1000, R~5000 and R ~ 10000 across the range 3300 Å to 9600 Å.

Full spectral coverage is possible in a single exposure with the low-resolution gratings.

The fibre spectra are recorded onto the 2K x 4K E2V CCDs with light dispersed along the 2K axis (not the 4K axis).

Same spectrograph used for 2dF or SAMI observations.


https://www.aao.gov.au/science/instruments/current/AAOmega

https://www.aao.gov.au/science/instruments/current/AAOmega


KOALA uses a double microlens array to feed the fibres. Although it is possible to feed a fibre array directly by placing it at the (magnified) focal plane, a microlens array offers 2 significant advantages:


1. A microlens array has close to 100% filling-factor (96% for KOALA), whereas a fibre array has a limited filling factor due to fibre cladding and packing.

2. A microlens array can be used to form a pupil-image on the face of the fibre, and therefore the coupling into the fibre is more efficient because both the pupil image size and the focal ratio can be matched to those required for efficient coupling into the fibre.

The KOALA micro lens arrays. The top image shows the SUSS hexagonal lenslets which face the sk, with a 100-micron grid overlaid. The bottom

image shows the second, circular lenslet array which faces the fibres.


KOALA offers a rectangular field of view with a selectable scale. The 1000 lenslets of the focal plane are laid out in a rectangle of 40 x 25 lenslets, an aspect ratio of 0.54.



The field is oriented such that at position angle of 0º, the long axis is east-west. The position angle is measured north-through east.


Raw data obtained by AAOmega using KOALA

• Single 30 min exposure of Blue Compact Dwarf Galaxy POX 4

• Blue arm using 580V grating (3650 - 5700 Å)

• Wide f ie ld : 27.4” x 50.6” with 1.25” spatial sampling

Raw data obtained by AAOmega using KOALA

• Single 30 min exposure of Blue Compact Dwarf Galaxy POX 4

• Blue arm using 580V grating (3650 - 5700 Å)


2dFdr is the AAO’s generic data reduction package for all of the observatory’s fibre based spectrographs. 2dFdr currently has modes that reduce data for a number of instruments including 2dF, SPIRAL, KOALA and SAMI feeds for AAOmega, 2dF+HERMES, and 6dF on the UK Schmidt.

Reducing AAOmega data: 2dFdr software

https://www.aao.gov.au/science/software/2dfdr

https://www.aao.gov.au/science/software/2dfdr


Once bias, dark, arc and flat-field frames are obtained, producing the wavelength- calibrated, full reduced frame just takes few minutes (auto-reduction pipeline).

Reducing AAOmega data: 2dFdr software

Reduced single 30 min blue (580V) frame produced by 2dFdr of POX 4. The resulting fits file has a size of 2048 (spectral axis) x 1000 (spaxels)


It is recommended to slightly offset the field between individual frames to avoid dead spaxels. This means individual frames can’t be directly combined using 2dFdr….

Problem: Avoiding dead spaxels

A Python script that provides offsets between spaxels for a given position angle.


I’m currently developing new Python scripts that combine and/or mosaic observations of a single source, deal with the spatial rebinning of the data onto a square spatial grid (i.e. cubing), and correct for atmospheric differential refraction. I expect these scripts to be completely functional by Semester 17A.

Solution: Python scripts


Combined data for 3 x 1800 s exposures of POX 4 using the 580V grating. The resulting fits file has a size of 2048 (spectral axis) x 1107 (spaxels). This is still work in progress…

Python scripts to get KOALA combined data


Map of the [O III] 5007 emission in POX 4



Map of the [O III] 5007 emission in POX 4, identifying spaxel 318



Wavelength-calibrated (but not flux-calibrated) of spaxel 318 (POX 4 centre)



Combined data for 3 x 1800 s exposures of POX 4 using the 1000R grating. The resulting fits file has a size of 2048 (spectral axis) x 1107 (spaxels). This is still work in progress…



Map of the H-alpha emission in POX 4, identifying spaxel 309



SummaryKOALA is a wide-field, high efficiency, integral field unit (IFU) designed for use with the bench mounted AAOmega spectrograph on the 3.9m AAT.

The double beam AAOmega spectrograph provides user selectable wavelength coverage and resolution using a series of movable, interchangeable gratings.

KOALA has 1000 hexagonal lenslets arranged in a rectangular array.

The field of view is selectable:

15.3” x 28.3”, with 0.7” spatial sampling 27.4” x 50.6”, with 1.25” spatial sampling

2dFdr software + new Python scripts can provide a ready-to-analyze SCIENCE frame in few minutes (Python scripts are still under developing but ready for 17A).

EVERYONE can apply for time at the AAT (regular or service mode)

Please contact me if you are interested on using this instrument!

Ángel López-Sánchez, KOALA / AAOmega instrument scientist [email protected]

KOALA: Kilofibre Optical AAT Lenslet Arrayastro.ft.uam.es › selgifs › uam2016 › slides ›...

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