The Gemini High Resolution Optical Spectrograph (GHOST) is a dual-object integral-field unit fed echelle spectrograph currently under construction by an Australian-led consortium including the Australian National University (ANU), the Australian Astronomical Observatory (AAO) and Canada’s Herzberg Astronomy and Astrophysics Research Center. The instrument control software for GHOST is under development by ANU. A brief overview of the relevant instrument subsystems is presented from the point of view of instrument control, along with a high-level overview of the software design. We discuss the operational concepts that have required specific software solutions, including IFU positioner collision avoidance, focal plane image reconstruction, and the guiding loop. We provide details of the various screens in the Acceptance Test and Engineering User Interface, showing how they support the operational concepts. The project comprises a variety of software technologies, including the Gemini Instrument Application Programmer Interface (GIAPI), ANU CICADA software, and various off-the-shelf packages. We discuss the use of these technologies, and our experiences with using them. The various different hardware devices also require specific software support, and we discuss our experiences with vendor-supplied libraries and code. We conclude with a brief outline of the development process, together with a discussion of successes and challenges.
We report the design evolution for the GMT Integral Field Spectrograph, (GMTIFS). To support the range of operating modes – a spectroscopic channel providing integral field spectroscopy with variable spaxel scales, and a parallel imaging channel Nyquist sampling the LTAO corrected field of view - the design process has focused on risk mitigation for the demanding operational tolerances. We summarise results from prototype components, confirming concepts are meeting the necessary specifications. Ongoing review and simulation of the scientific requirements also leads to new demonstrations of the science that will be made possible with this new generation of high performance AO assisted instrumentation.
GHOST is a high resolution spectrograph system currently being built for the Gemini South Observatory in Chile. In the Cassegrain unit, the observational targets are acquired on integral field units and guided during science exposures, feeding the fiber cable to the temperature-stabilized echelle spectrograph. The Cassegrain unit is mounted on the Gemini telescope, and consists of a main structural plate, the two object positioners and ballast frame. The image from each of the two science beams passes through a field lens and a mini-atmospheric dispersion corrector and is then captured by the integral field unit. The positioner moves each corrector-integral field unit assembly across the focal surface of the telescope. The main structural plate provides the interface for the positioner and ballast frame to the telescope structure. In this paper we describe the final design and assembly of the GHOST Cassegrain unit and report on the outcome of on-sky testing at the telescope in Chile.
The Gemini High-Resolution Optical SpecTrograph (GHOST) is the newest instrument chosen for the Gemini South telescope. It is being developed by a collaboration between the Australian Astronomical Observatory (AAO), the NRC - Herzberg in Canada and the Australian National University (ANU). Using recent technological advances and several novel concepts it will deliver spectroscopy with R>50,000 for up to 2 objects simultaneously or R>75,000 for a single object. GHOST uses a fiber-image-slicer to allow use of a much smaller spectrograph than that nominally required by the resolution-slit–width product. With its fiber feed, we expect GHOST to have a sensitivity in the wavelength range between 363-950 nm that equals or exceeds that of similar directly-fed instruments on world-class facilities. GHOST has entered the build phase. We report the status of the instrument and describe the technical advances and the novel aspects, such as the lenslet-based slit reformatting. Finally, we describe the unique scientific role this instrument will have in an international context, from exoplanets through stellar elemental abundances to the distant Universe. Keywords: Gemini, spectrograph, spectroscopy, ́echelle, high resolution, radial velocity, fiber image slicer, integral field unit.
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.
The recent availability of large format near-infrared detectors with sub-election readout noise is revolutionizing our approach to wavefront sensing for adaptive optics. However, as with all near-infrared detector technologies, challenges exist in moving from the comfort of the laboratory test-bench into the harsh reality of the observatory environment. As part of the broader adaptive optics program for the GMT, we are developing a near-infrared Lucky Imaging camera for operational deployment at the ANU 2.3 m telescope at Siding Spring Observatory. The system provides an ideal test-bed for the rapidly evolving Selex/SAPHIRA eAPD technology while providing scientific imaging at angular resolution rivalling the Hubble Space Telescope at wavelengths λ = 1.3-2.5 μm.
The new Gemini High Resolution Optical Spectrograph (GHOST) will be controlled with software developed against the new Gemini software framework - the Gemini Instrument Application Programmer Interface (GIAPI). The developers describe their experience using this framework and compare it to control systems developed for earlier Gemini instruments using the original Gemini Core Instrument Control System (CICS) framework.
To achieve the high adaptive optics sky coverage necessary to allow the GMT Integral-Field Spectrograph (GMTIFS) to access key scientific targets, the on-instrument adaptive-optics wavefront-sensing (OIWFS) system must patrol the full 180 arcsecond diameter guide field passed to the instrument. The OIWFS uses a diffraction limited guide star as the fundamental pointing reference for the instrument. During an observation the offset between the science target and the guide star will change due to sources such as flexure, differential refraction and non-sidereal tracking rates. GMTIFS uses a beam steering mirror to set the initial offset between science target and guide star and also to correct for changes in offset. In order to reduce image motion from beam steering errors to those comparable to the AO system in the most stringent case, the beam steering mirror is set a requirement of less than 1 milliarcsecond RMS. This corresponds to a dynamic range for both actuators and sensors of better than 1/180,000.
The GMTIFS beam steering mirror uses piezo-walk actuators and a combination of eddy current sensors and interferometric sensors to achieve this dynamic range and control. While the sensors are rated for cryogenic operation, the actuators are not. We report on the results of prototype testing of single actuators, with the sensors, on the bench and in a cryogenic environment. Specific failures of the system are explained and suspected reasons for them. A modified test jig is used to investigate the option of heating the actuator and we report the improved results. In addition to individual component testing, we built and tested a complete beam steering mirror assembly. Testing was conducted with a point source microscope, however controlling environmental conditions to less than 1 micron was challenging. The assembly testing investigated acquisition accuracy and if there was any un-sensed hysteresis in the system. Finally we present the revised beam steering mirror design based on the outcomes and lessons learnt from this prototyping.
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) 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.
Engineers in several observatories are now designing the next generation of optical telescopes, the Extremely Large
Telescopes (ELT). These are very complex machines that will host sophisticated astronomical instruments to be used for
a wide range of scientific studies.
In order to carry out scientific observations, a software infrastructure is required to orchestrate the control of the multiple
subsystems and functions. This paper will focus on describing the considerations, strategies and main issues related to
the definition and analysis of the software requirements for the ELT's Instrument Control System using modern
development processes and modelling tools like SysML.
This paper describes the software systems implemented for the wide-field, automated survey telescope, SkyMapper. The
telescope is expected to operate completely unmanned and in an environment where failures will remain unattended for
several days. Failure analysis was undertaken and the control system extended to cope with subsystem failures,
protecting vulnerable detectors and electronics from damage. The data acquisition and control software acquires and
stores 512 MB of image data every twenty seconds. As a consequence of the short duty cycle, the preparation of the
hardware subsystems for the successive images is undertaken in parallel with the imager readout. A science data pipeline
will catalogue objects in the images to produce the Southern Sky Survey.
The RSAA CICADA data acquisition and control software package uses an object-oriented approach to model
astronomical instrumentation and a layered architecture for implementation. Emphasis has been placed on building
reusable C++ class libraries and on the use of attribute/value tables for dynamic configuration. This paper details how
the approach has been successfully used in the construction of the instrument control software for the Gemini NIFS and
GSAOI instruments. The software is again being used for the new RSAA SkyMapper and WiFeS instruments.
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 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.
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.