Peter J. Young

Gemini multiconjugate adaptive optics system review – II. Commissioning, operation and overall performance

The Gemini Multi-conjugate Adaptive Optics System - GeMS, a facility instrument mounted on the Gemini South telescope, delivers a uniform, near di↵raction limited images at near infrared wavelengths (0.95 µm - 2.5 µm) over a field of view of 120 00 . GeMS is the first sodium layer based multi laser guide star adaptive optics system used in astronomy. It uses five laser guide stars distributed on a 60 00 square constellation to measure for atmospheric distortions and two deformable mirrors to compensate for it. In this paper, the second devoted to describe the GeMS project, we present the commissioning, overall performance and operational scheme of GeMS. Performance of each sub-system is derived from the commissioning results. The typical image quality, expressed in full with half maximum, Strehl ratios and variations over the field delivered by the system are then described. A discussion of the main contributor to performance limitation is carried-out. Finally, overheads and future system upgrades are described.

GeMS: first on-sky results

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.

Results from the commissioning of the Gemini South Adaptive Optics Imager (GSAOI) at Gemini South Observatory

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 this conference.

Using ODGWs with GSAOI: software and firmware implementation challenges

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.

Achieving design reuse: a case study

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.

The Gemini High-Resolution Optical SpecTrograph (GHOST)

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.

GHOST instrument control software: a progress report

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.

Design evolution of the Giant Magellan Telescope Integral Field Spectrograph, GMTIFS

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.

Final design and assembly of the GHOST Cassegrain unit

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.

GMTIFS: the adaptive optics beam steering mirror for the GMT integral-field spectrograph

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.