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Instrumentation Status for the AAT

General Information

The most detailed information on all AAT instrumentation can be found on the AAO Instrumentation Pages.

Queries can be directed to the relevant instrument scientists. These are (usernames in brackets - all email should be sent to user -@- aao.gov.au):

Status of Common-User Instruments


AAOmega + 2dF Multi-Object Spectroscopy

NEW: From Semester 2013A onward, the new HERMES/AAOmega dual fibres are in use for 2dF. They offer more even throughput and improved fringing performance.

AAOmega is a dual-beam, bench-mounted spectrograph for the 2dF top end. Science Verification results with 2dF can be found in the February 2006 AAO Newsletter, and more informatation can be found in the AAOmega general pages.

The throughput of both the red and blue cameras of AAOmega has recently been re-determined, and the AAOmega MOS S/N calculator updated to reflect this. All applicants should re-determine their exposure times accordingly.

Depending on the complexity of the field configuration and the number of fibre moves required, applicants can expect up to 5 seconds to position a single fibre, and that each field will require a minimum of 45 min, including overheads.

An alternate dichroic, procured by the WiggleZ team and the AAO, is available to all AAOmega users. This dichroic shifts the transition wavelength between the blue and red cameras from 5700 Å to 6700 Å, and allows full wavelength coverage with the 385R grating right out to ~9500 Å. The dichroic change occurs over +/-200 Å. The 5700 Å dichroic is of exceptional quality, with a smooth monotonic changeover, while the 6700 Å is smooth, but not monotonic. Additionally, there are two 20% troughs in the reflected beam at 4815 and 4905 Å. The optics are in a slowly converging beam and so these features are not removed by a simple flat field observation. A local averaging option in the 2dfdr software alleviates the problem somewhat. Applicants considering using the 6700 Å dichroic should contact Andy Green before applying, and then indicate their choice in their proposal and Instrument Request Form.

All 2dF MOS applications must pay particular attention to the quality of their astrometry, and should give details about this in their proposal. Recent improved mapping of distortions introduced by the gripper gantry have improved the reliability of fibre positioning down to 0.3 arcsec or better. AAOmega+2dF field plates have 8 guide fibres and 392 science fibres. Mean sky fibre subtraction has achieved residuals as low as 1%, so observers considering the use of Nod & Shuffle or Cross-Beam Switching techniques should discuss their needs with Andy Green prior to submitting their proposal, to ensure that the extra workload for the user, and significant exposure time overheads (factors of between sqrt(2) and 4, depending on N+S mode) involved, are commensurate with the improvement in data quality.

In order to allow sufficient time for run preparation, all configuration (.fld) files must be forwarded to your Support Astronomer no later than one month before the scheduled observing run. Failure to do so may result in forfeiting the allocated time.

Further details about the capabilities of AAOmega in 2dF MOS mode are available, as well as a list of available gratings.


AAOmega + SPIRAL Integral Field Unit

AAOmega is a dual-beam, bench-mounted spectrograph which can also be used with the SPIRAL IFU at the Auxiliary Cassegrain focus. The SPIRAL Integral Field Unit (IFU) is a 512 element fibre feed to AAOmega, and permits 3D spectroscopy over a field-of-view of 22.4 x 11.2 arcsec at a spatial sampling of 0.7 arcsec. Science Verification results can be found in the August 2006 AAO Newsletter.

The throughput of both the red and blue cameras of AAOmega has recently been re-determined, and the AAOmega IFU S/N calculator updated to reflect this. All applicants should re-determine their exposure times accordingly. Users should note the U band sensitivity is comparatively poor due to components used in the construction of the SPIRAL IFU.

An alternate dichroic, procured by the WiggleZ team and the AAO, is now available to all AAOmega users. This dichroic shifts the transition wavelength between the blue and red cameras from 5700 Å to 6700 Å, and allows full wavelength coverage with the 385R grating right out to ~9500 Å. The dichroic change occurs over +/-200 Å. The 5700 Å dichroic is of exceptional quality, with a smooth monotonic changeover, while the 6700 Å is smooth, but not monotonic. Additionally, there are two 20% troughs in the reflected beam at 4815 and 4905 Å. The optics are in a slowly converging beam and so these features are not removed by a simple flat field observation. A local averaging option in the 2dfdr software alleviates the problem somewhat. Applicants considering using the 6700 Å dichroic should contact Andy Green before applying, and then indicate their choice in their proposal and Instrument Request Form.

Further details about the capabilities of AAOmega in SPIRAL IFU modes are available, as well as a list of available gratings.


HERMES + 2dF MOS

HERMES commissioning is planned for Semester 13A, and it is being offered for use in 13B in shared-risk mode. Prospective observers should be aware that instrument capabilities have not been thoroughly assessed yet.

HERMES is a four-channel, bench-mounted high-resolution spectrograph for use with the 2dF top end. The wavelength rangs of the four channels are fixed at 4718-4903 Å, 5649-5873 Å, 6481-6739 Å and 7590-7890 Å. The spectral resolution is nominally R~28,000, which can be raised to R~45,000 with the use of a slitmask in the spectrograph. Instrument commissioning is planned for Semester 13A. Questions about current instrument status should be directed to Gayandhi de Silva.

All 2dF MOS applications must pay particular attention to the quality of their astrometry, and should give details about this in their proposal. Recent improved mapping of distortions introduced by the gripper gantry have improved the reliability of fibre positioning down to 0.3 arcsec or better. HERMES+2dF field plates have 8 guide fibres and 392 science fibres.

In order to allow sufficient time for run preparation, all configuration (.fld) files must be forwarded to your Support Astronomer no later than one month before the scheduled observing run. Failure to do so may result in forfeiting the allocated time.


IRIS2

IRIS2 is an infrared imager and spectrograph which can be used for either imaging or moderate resolution spectroscopy in the wavelength range from 1.0 to 2.4 microns. The detector is a HgCdTe array of 1024 x 1024 pixel format. IRIS2 is normally used with the f/8 secondary mirror, giving a pixel scale of 0.45"/pixel and a field of view of 7.7' x 7.7'. Broad-band (J, H, Ks and K) and a range of narrow-band filters are available. Both long-slit, and multi-object (using multi-slit masks) spectroscopy (MOS) in the J, H, and K-bands at R~2400 can be carried out. All standard imaging, and point-source spectroscopy data are pipeline-processed by the ORAC-DR system.

IRIS2 MOS makes multi-object observations over the IRIS2 field available for a maximum of three masks per installation of IRIS2 on the telescope. In practice, this translates to a maximum of three masks per lunation, making it optimally suited to deep observations of multiple targets. In the event of multiple proposals exceeding this maximum limit, the usual procedure of preferring proposals with higher grades will be followed. Note that separate masks are needed to observe the same field in H, as in J or K. Prospective IRIS2 MOS applicants should contact Angel Lopez-Sanchez to discuss their requirements prior to submitting a proposal.

Information on the capabilities of IRIS2, including the information required for S/N calculations for imaging and spectroscopy, is provided on the IRIS2 Web pages, or contact Angel Lopez-Sanchez with any queries.


UCLES

UCLES is a cross-dispersed échelle spectrograph located at the coudé focus, offering a resolution of 40,000-120,000 depending on the slit width and CCD binning. The 79 l/mm grating gives slightly less wavelength coverage than the 31.6 l/mm grating, but offers a longer slit for extended objects, or better sky subtraction on fainter targets. Switching between the two gratings is trivial. The EEV2 2K x 4K CCD should be the detector of choice for most UCLES programs when working blueward of H-alpha (6563 Å). At longer wavelengths, the significant fringing of the EEV2 could be a problem (see the EEV2 Web page), and the MITLL3 detector has better red quantum efficiency in any case (though binning is not possible with the MITLL3).

Both UCLES itself, and the attached CCD detector, are controlled by an integrated Linux/VME-based GUI, which allows automated observing sequences and independent telescope control, among other things. Information on this interface is available in the ODC Users Guide in the UCLES Cookbook. Prospective UCLES users should contact the instrument scientist, Gayandhi de Silva, for more information.

CYCLOPS2: UCLES (with the 79 l/mm echelle only) can be used with the CYCLOPS2 cassegrain fibre-feed to observe single objects. It provides 50% improved resolution over a typical 1" wide slit, along with about 50% higher photon collecting power in typical AAT seeing. Previous issues with instrumental flexure have now been resolved (as of Feb 2011), and flat-fielding and arc calibration strategies are well understood. The UCLES instrument page carries more detailed information on the use of CYCLOPS2.


UHRF

The UHRF is a separate échelle spectrograph located in the same coudé room as UCLES. It offers ultra high resolution over very small spectral regions, using an image slicer in place of the slit. UHRF is generally used with the EEV2 detector, at 3E5, 6E5, and 1E6 resolving power. The MITLL3 CCD cannot be binned, so is less suited to UHRF except when fringing of the EEV2 detector in the red may limit the S/N achievable (contact Stephen Marsden for further information). Note that it is also possible to observe at 100,000 resolution directly through a 0.6 arcsec slit at 3E5, with a 4-5x gain in throughput over the use of the image slicer, depending on the seeing. Because UHRF's image slicer comes after the 1.5" square entrance aperture, UHRF throughput is rather more seeing-dependent than UCLES.

As with UCLES, UHRF and its detector are controlled by an integrated GUI, which allows automated observing sequences and independent telescope control, among other things. Information on this interface is available in the ODC Users Guide in the UHRF Cookbook. Prospective UHRF users should contact the instrument scientist, Gayandhi de Silva, for more information.

CYCLOPS2: Note that UHRF can not be used with CYCLOPS2. Further information can be found at the UCLES instrument pages.

Visitor Instruments

Proposals for the use of visitor instruments on the AAT are welcome. However. all applicants seeking to use a visitor instrument must first obtain the permission of the Director (director -@- aao.gov.au), even if that instrument has been used previously.

Sarah Martell, AAT Technical Secretary to ATAC, aatts -@- aao.gov.au
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