The Giant Magellan Telescope (GMT) Integral-Field Spectrograph (GMTIFS)c is one of six potential first-light
instruments for the 25m-diameter Giant Magellan Telescope. The Australian National University has completed a
Conceptual Design Study for GMTIFS. The science cases for GMTIFS are summarized, and the instrument capabilities
and design challenges are described. GMTIFS will be the work-horse adaptive-optics instrument for GMT. It contains an
integral-field spectrograph (IFS) and Imager accessing the science field, and an On-Instrument Wave-Front Sensor
(OIWFS) that patrols the 90 arcsec radius guide field. GMTIFS will address a wide range of science from epoch of
reionization studies to forming galaxies at high redshifts and star and planet formation in our Galaxy. It will fully exploit
the Laser Tomography Adaptive Optics (LTAO) system on the telescope. The tight image quality and positioning
stability requirements that this imposes drive the design complexity. Some cryogenic mechanisms in the IFS must set to
~ 1 μm precision. The Beam-Steering mechanism in the OIWFS must set to milli-arcsecond precision over the guide
field, corresponding to ~ 1 μm precision in the f/8 focal plane. Differential atmospheric dispersion must also be corrected
to milli-arcsecond precision. Conceptual design solutions addressing these and other issues are presented and discussed.
GeMS, the Gemini Laser Guide Star Multi-Conjugate Adaptive Optics facility system, has seen first light in December 2011, and has already produced images with H band Strehl ratio in excess of 35% over fields of view of 85x85 arcsec, fulfilling the MCAO promise. In this paper, we report on these early results, analyze trends in performance, and concentrate on key or novel aspects of the system, like centroid gain estimation, on-sky non common path aberration estimation. We also present the first astrometric analysis, showing very encouraging results.
We present the results from the commissioning of the Gemini South Adaptive Optics Imager (GSAOI). Capable
of delivering diffraction limited images in the near-infrared, over an 85′′
×85′′ square field-of-view, GSAOI was
designed for use with the Gemini Multi-Conjugate Adaptive Optics (GeMS) system in operation at the Gemini
South Observatory. The instrument focal plane, covered by an array of four HAWAII-2RG detectors, contains
4080×4080 pixels and has a plate scale of 0.02′′ – thus capitalizing on the superb image quality delivered by both
the all-refractive optical design of GSAOI and the Gemini South MCAO system. Here, we discuss our preliminary
findings from the GSAOI commissioning, concentrating on detector characterization, on-sky performance and
system throughput. Further specifics about the Gemini MCAO system can be found in other presentations at
The Gemini South Adaptive Optics Imager (GSAOI) to be used with the Multi-Conjugate Adaptive Optics (MCAO) system at Gemini South is currently in the final stages of assembly and testing. GSAOI uses a suite of 26 different filters, made from both BK7 and Fused Silica substrates. These filters, located in a non-collimated beam, work as active optical elements.
The optical design was undertaken to ensure that both the filter substrates both focused longitudinally at the same point. During the testing of the instrument it was found that longitudinal focus was filter dependant. The methods used to investigate this are outlined in the paper. These investigations identified several possible causes for the focal shift including substrate material properties in cryogenic conditions and small amounts of residual filter power.
Large-area near-infrared focal-plane detector arrays constructed from one and four Rockwell Science Center HAWAII-
2RG HgCdTe detectors have been characterized for use in the NIFS and GSAOI instruments recently developed for the
Gemini telescopes by the Australian National University. We present details of the detector characterization and
compare the performance of five distinct devices with respect to read noise, dark current, and stability in systems based
on ARC/SDSU Gen-3 controllers. Advanced operating modes of the H2RG were implemented including enhanced
clocking and independent On-Detector Guide Windows for GSAOI. Detector performance using these features and the
impact of multiple guide-window reads on long integrations are explored. We also discuss measurement of intra-pixel
coupling and its impact on pixel-well capacity, gain, and image quality for these devices.
The Wide Field Spectrograph (WiFeS) is a high-throughput double-beam
image-slicing spectrograph that will operate over the visible
wavelength range 320nm to 1000nm. Designed by the Australian National
University's Research School of Astronomy and Astrophysics (RSAA) at
Mount Stromlo, WiFeS is based on an Integral Field Unit (IFU) and
Volume Phased Holographic (VPH) grating technology.
Central to the IFU design is a visible wavelength image
slicer. Traditionally, such a slicer has been difficult to realise,
due to the requisite high surface quality demanded to reduce scatter
from each slice.
In this paper, we discuss both the novel design and manufacture of the
WiFeS slicer assembly. Preliminary results are presented that clearly
demonstrate the effectiveness of the design.
WiFeS is a powerful integral field, double-beam, concentric, image-slicing spectrograph designed to deliver excellent thoughput, precision spectrophotometric performance and superb image quality along with wide spectral coverage throughout the 320-1000 nm wavelength region. It is currently under construction at the Research School of Astronomy and Astrophysics of the Australian National University (ANU), and will be mounted on the ANU 2.3m telescope at Siding Spring Observatory. It will provide a 25x31 arc sec field with 0.5 arc sec sampling along each of twenty five 31x1.0 arc sec slitlets. The output format is arranged to match the 4096x4096 pixel CCD detectors in each of two cameras individually optimized for the blue and the red ends of the spectrum, respectively. A process of "interleaved nod-and-shuffle" will be applied to permit quantum noise-limited sky subtraction. Using VPH gratings, spectral resolutions modes of 3000 and 7000 will be provided. The full spectral range is covered in a single exposure in the R=3000 mode, and in two exposures in the R=7000 mode. The use of transmissive coated optics, VPH gratings and optimized mirror coatings ensures a throughput (including telescope and atmosphere) that peaks above 30%. The concentric image-slicer design ensures an excellent and uniform image quality across the full field. To maximize the scientific return, the whole instrument is configured for remote observing, pipeline data reduction, and the accumulation of calibration image libraries.