Instrument development for the 24m Giant Magellan Telescope (GMT) is described: current activities, progress, status, and schedule. One instrument team has completed its preliminary design and is currently beginning its final design (GCLEF, an optical 350-950 nm, high-resolution and precision radial velocity echelle spectrograph). A second instrument team is in its conceptual design phase (GMACS, an optical 350-950 nm, medium resolution, 6-10 arcmin field, multi-object spectrograph). A third instrument team is midway through its preliminary design phase (GMTIFS, a near-IR YJHK diffraction-limited imager/integral-field-spectrograph), focused on risk reduction prototyping and design optimization. A fourth instrument team is currently fabricating the 5 silicon immersion gratings needed to begin its preliminary design phase (GMTNIRS, a simultaneous JHKLM high-resolution, AO-fed, echelle spectrograph). And, another instrument team is focusing on technical development and prototyping (MANIFEST, a facility robotic, multifiber feed, with a 20 arcmin field of view). In addition, a medium-field (6 arcmin, 0.06 arcsec/pix) optical imager will support telescope and AO commissioning activities, and will excel at narrow-band imaging. In the spirit of advancing synergies with other groups, the challenges of running an ELT instrument program and opportunities for cross-ELT collaborations are discussed.
GMTIFS is the first-generation adaptive optics integral-field spectrograph for the GMT, having been selected through a competitive review process in 2011. The GMTIFS concept is for a workhorse single-object integral-field spectrograph, operating at intermediate resolution (R~5,000 and 10,000) with a parallel imaging channel. The IFS offers variable spaxel scales to Nyquist sample the diffraction limited GMT PSF from λ ~ 1-2.5 μm as well as a 50 mas scale to provide high sensitivity for low surface brightness objects. The GMTIFS will operate with all AO modes of the GMT (Natural guide star - NGSAO, Laser Tomography – LTAO, and, Ground Layer - GLAO) with an emphasis on achieving high sky coverage for LTAO observations. We summarize the principle science drivers for GMTIFS and the major design concepts that allow these goals to be achieved.
Instrument development for the 25 m class optical/infrared Giant Magellan Telescope (GMT) is actively underway. Two
instruments have begun their preliminary design phase: an optical (350-1000 nm) high resolution and precision radial
velocity echelle spectrograph (G-CLEF), and a near-IR (YJHK) diffraction-limited imager/integral-field-spectrograph
(GMTIFS). A third instrument will begin its design phase in early 2015: an optical (370-1000 nm) low-to-medium
resolution multi-object spectrograph (GMACS). Two other instrument teams are focusing on prototypes to demonstrate
final feasibility: a near-to-mid-IR (JHKLM) high resolution diffraction-limited echelle (GMTNIRS) spectrograph, and a
facility robotic multi-fiber-feed (MANIFEST). A brief overview of the GMT instrumentation program is presented:
current activities, progress, status, and schedule, as well as a summary of the facility infrastructure needed to support the
To achieve the high adaptive optics sky coverage necessary to allow the GMT Integral-Field Spectrograph to
access key scientific targets, the on-instrument adaptive-optics wavefront-sensing system must patrol the full 180
arcsecond diameter guide field passed to the instrument. Starlight must be held stationary on the wavefront
sensor (accounting for flexure, differential refraction and non-sidereal tracking rates) to ~ 1 milliarcsecond to
provide the stable position reference signal for deep AO observations and avoid introducing image blur. Hence a
tight tolerance of 1/180,000 is placed on the positioning and encoding accuracy for the cryogenic On-Instrument
Wave-Front Sensor feed. GMTIFS will achieve this requirement using a beam-steering mirror system as an
optical relay for starlight from across the accessible guide field. The system avoids hysteresis and backlash by
eliminating friction and avoiding gearing while maintaining high setting speed and accuracy with a precision
feedback loop. Here we present the design of the relay system and the technical solution deployed to meet the
challenging specifications for drive rate, accuracy and positional encoding of the beam-steering system.
The Gemini High-Resolution Optical SpecTrograph (GHOST) is the newest instrument being developed for the Gemini telescopes, in a collaboration between the Australian Astronomical Observatory (AAO), the NRC - Herzberg in Canada and the Australian National University (ANU). We describe the process of design optimisation that utilizes the unique strengths of the new partner, NRC - Herzberg, the design and need for the slit viewing camera system, and we describe a simplification for the lenslet-based slit reformatting. Finally, we out- line the updated project plan, and describe the unique scientific role this instrument will have in an international context, from exoplanets through to the distant Universe.
The Gemini South Adaptive-Optics Imager (GSAOI) has recently been commissioned on the Gemini South telescope.
Designed for use with the Gemini GeMS Multi-Conjugate Adaptive Optics System, GSAOI makes use of the HAWAII-
2RG (H2RG) On-Detector Guide Window (ODGW) feature where guide windows positioned in each of the four H2RG
detectors provide GeMS with tip-tilt and flexure corrections. This paper concentrates on the complex software and
firmware required for operating the ODGWs and for delivering the performance required by GeMS. Software
architecture, algorithms, performance and the implementation platform for the current on-telescope solution are detailed.
The Giant Magellan Telescope (GMT) is a 25.4-m optical/infrared telescope constructed from seven 8.4-m primary
mirror segments. The collecting area is equivalent to a 21.6-m filled aperture. The instrument development program was
formalized about two years ago with the initiation of 14-month conceptual design studies for six candidate instruments.
These studies were completed at the end of 2011 with a design review for each. In addition, a feasibility study was
performed for a fiber-feed facility that will direct the light from targets distributed across GMT's full 20 arcmin field of
view simultaneously to three spectrographs. We briefly describe the features and science goals for these instruments, and
the process used to select those instruments that will be funded for fabrication first. Detailed reports for most of these
instruments are presented separately at this meeting.
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.
The Gemini High-Resolution Optical SpecTrograph (GHOST) will fill an important gap in the current suite of Gemini
instruments. We will describe the Australian Astronomical Observatory (AAO)-led concept for GHOST, which consists
of a multi-object, compact, high-efficiency, fixed-format, fiber-fed design. The spectrograph itself is a four-arm variant
of the asymmetric white-pupil echelle Kiwispec spectrograph, Kiwisped, produced by Industrial Research Ltd. This
spectrograph has an R4 grating and a 100mm pupil, and separate cross-disperser and camera optics for each of the four
arms, carefully optimized for their respective wavelength ranges. We feed this spectrograph with a miniature lensletbased
IFU that sub-samples the seeing disk of a single object into 7 hexagonal sub-images, reformatting this into a slit
with a second set of double microlenses at the spectrograph entrance with relatively little loss due to focal-ratio
degradation. This reformatting enables high spectral resolution from a compact design that fits well within the relatively
tight GHOST budget. We will describe our baseline 2-object R~50,000 design with full wavelength coverage from the
ultraviolet to the silicon cutoff, as well as the high-resolution single-object R~75,000 mode.
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
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.
The Giant Magellan Telescope (GMT) is a 24.5m diameter optical/infrared telescope. Its seven 8.4m primary mirrors
give it a collecting area equivalent to a 21.4m filled aperture. The ten GMT partners are constructing the telescope at the
Las Campanas Observatory in Chile with first light planned for the end of 2018. In this paper, we describe the plans for
the first-generation focal plane instrumentation for the telescope. The GMTO Corporation has solicited studies for
instruments capable of carrying out the broad range of objectives outlined in the GMT Science Case. Six instruments
have been selected for 14 month long conceptual design studies. We briefly describe the features of these instruments
and give examples of the major science questions that they can address.
The design of the adaptive optics (AO) system for the GMT is currently being developed. The baseline system is
planned around a segmented adaptive secondary mirror (ASM), with elements similar in size to current ASM's for 8 m
telescopes. A facility wavefront sensing system is planned to provide AO correction at several science instrument ports.
The AO system will contain a subsystem dedicated to controlling the relative phases between the seven segments of the
GMT aperture. The anticipated modes include natural guide star, laser tomography, and ground layer adaptive optics. A
cooled optical relay is described to provide baffling and reimaging of the focal plane to the various science ports. The
laser projection system will use six beacons on an adjustable radius to support both diffraction-limited and ground layer
correction modes. Modeling work, as well as science instrument design development will be integrated with this design
effort to develop a concept that provides efficient diffraction-limited performance and seeing-improved capabilities for
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.
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.
The Gemini South Adaptive Optics Imager (GSAOI) is the science camera and commissioning instrument for the Multi-Conjugate Adaptive Optics (MCAO) system on the Gemini South telescope. GSAOI is required to deliver diffraction-limited performance at near-infrared wavelengths over a 85"×85" field of view. It must be delivered on a short timescale commensurate with MCAO delivery. GSAOI will use a high throughput, all-refractive optical design and a mosaic of four HAWAII-2RG detectors to form an imager focal plane of 4080x4080 pixels with a fixed scale of 0.02"/pixel. The On-Detector Guide Window (ODGW) capability of the HAWAII-2RG detectors will be used for flexure monitoring and as near-infrared substitutes for MCAO natural guide star wave front sensors. The imager will include a pupil viewer for accurate alignment to MCAO and defocus lenses to measure wave front phase errors at the science detector using the curvature technique. Non-common path wave front errors will be nulled by setting the base shapes of the three MCAO deformable mirrors. The science drivers, performance predictions, optical design issues, and detector system for the instrument are described.
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.
The Gemini Near-infrared Integral Field Spectrograph (NIFS) will be used with the ALTAIR adaptive optics system on Gemini North. NIFS uses a reflective, concentric, integral field unit (IFU) to reformat its focal plane. The concentric IFU design integrates the IFU with the spectrograph collimator to form a dedicated IFU instrument. The IFU channels are identical and fanned about a single axis passing through the image slicer. The spherical optical surfaces of the spectrograph collimator are all concentric and centered on this fanning axis. The grating is also located on the fanning axis, and the system is arranged to produce coincident pupil images at the grating. In this way, each channel of the IFU performs as if it is on-axis. This avoids complications due to off-axis angles that are intrinsic to other reflective IFU designs.
NIFS is a near-infrared integral field spectrograph designed for near diffraction-limited imaging spectroscopy with the ALTAIR facility adaptive optics system on Gemini North. NIFS is currently under construction at the Research School of Astronomy and Astrophysics of the Australian National University. Commissioning is planned for 2003. NIFS uses a reflective concentric integral field unit to reformat its 3.0"x3.0" field-of-view into 29 slitlets each 0.1" wide with 0.04" sampling along each slitlet. The NIFS spectrograph has a resolving power of ~ 5300, which is large enough to significantly separate terrestrial airglow emission lines and resolve velocity structure in galaxies. The output format is matched to a 2048x2048 pixel Rockwell HAWAII-2 detector. The detector is read out through a SDSU-2 detector controller connected via a VME interface to the Gemini Data Handling System. NIFS is a fast-tracked instrument that reuses many of the designs of the Gemini Near-InfraRed Imager (NIRI); the cryostat, On-Instrument Wave Front Sensor, control system, and control software are largely duplicates.