Gabe Bloxham

The Planetary Nebula Spectrograph: The Green Light for Galaxy Kinematics

ABSTRACT Planetary nebulae (PNe) are now well established as probes of galaxy dynamics and as standard candles in distance determinations. Motivated by the need to improve the efficiency of planetary nebulae searches and the speed with which their radial velocities are determined, a dedicated instrument—the Planetary Nebula Spectrograph, or PN.S—has been designed and commissioned at the 4.2 m William Herschel Telescope. The high optical efficiency of the spectrograph results in the detection of typically ∼150 PNe in galaxies at the distance of the Virgo Cluster in one night of observations. In the same observation, the radial velocities are obtained with an accuracy of ∼20 km s \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcom...

GMT Integral-Field Spectrograph (GMTIFS) conceptual design

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.

CASPIR: A cryogenic array spectrometer imager for the MSSSO 2.3 m telescope

CASPIR is a near-infrared spectrometer/imager being built for the Mount Stromlo and Siding Spring Observatories’ 2.3 m telescope. The instrument is based on a SBRC 256x256 InSb detector array and uses AR-coated Sapphire, MgO, CaF2, and BaF2 optics to produce two imaging focal plane scales with 0.5″/pixel and 0.25″/pixel. Spectral resolving powers of ~ 500 will be achieved through a 1″ × 128″ slit with three grisms designed for the J, H, and K bands. IJ, JH, and HK cross-dispersed echelle grisms will achieve resolving powers of ~ 1100 through a 1″ × 15″ slit. Coronograph and imaging polarimetry modes will also be available. The various observing configurations are selected via five remotely controlled wheels. The instrument design and system architecture are discussed, and preliminary detector performance figures reported.

NIFS concentric integral field unit

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.

GMTIFS: deformable mirror environmental testing for the on-instrument wavefront sensor

GMTIFS requires a deformable mirror (DM) as part of its on-instrument wavefront sensor (OIWFS). The DM facilitates wavefront correction for the off-axis natural guide star, with the objective being to maximize the energy in the diffraction core and improve the signal-to-noise ratio of the guide star position measurement. It is essential that the OIWFS be positionally stable with respect to the science field. The use of J–K to observe the guide star, and thus the need to limit thermal background, essentially requires the DM in the OIWFS to be operated at or below −40°C. This is below the standard operating temperature range of currently available DMs. In cooperation with the manufacturers we are testing the performance of three DMs at temperatures from ambient to −45°C, or cooler. In the context of the OIWFS adequate stroke, open-loop positioning stability, hysteresis, interactuator surface figure and dynamic response are key performance criteria. A test system based around high spatial sampling of the DM aperture with a Shack-Hartmann wavefront sensor has been built. The opto-mechanical design permits a DM to be contained in a cryostat so that it may be cooled in isolation. We describe this test system and the test cases that are applied to the ALPAO DM-69, Boston MicroMachines 492DM and the IrisAO PTT111 deformable mirrors. Preliminary results at ambient temperatures are presented.

GMTIFS: The Giant Magellan Telescope integral fields spectrograph and imager

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.

Veloce Rosso: Australia's new precision radial velocity spectrograph

Veloce is an ultra-stable fibre-fed R4 echelle spectrograph for the 3.9 m Anglo-Australian Telescope. The first channel to be commissioned, Veloce ‘Rosso’, utilises multiple low-cost design innovations to obtain Doppler velocities for sun-like and M-dwarf stars at <1 ms -1 precision. The spectrograph has an asymmetric white-pupil format with a 100-mm beam diameter, delivering R>75,000 spectra over a 580-930 nm range for the Rosso channel. Simultaneous calibration is provided by a single-mode pulsed laser frequency comb in tandem with a traditional arc lamp. A bundle of 19 object fibres ensures full sampling of stellar targets from the AAT site. Veloce is housed in dual environmental enclosures that maintain positive air pressure at a stability of ±0.3 mbar, with a thermal stability of ±0.01 K on the optical bench. We present a technical overview and early performance data from Australias next major spectroscopic machine.

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.

Testing a prototype rotary mechanism for GMTIFS

The GMTIFS instrument requires multiple rotary mechanisms that will operate in a cryogenic environment. Angular precision up to one arc-second is required without the use of IR sources as part of an encoder. A general design that uses an annular conical rim bearing supported by three pairs of tapered pinch rollers has been proposed. One pair of pinch rollers is mounted on a flexure hinge to provide preload and accommodate thermal expansion. A pair of off set cylindrical cams carried by the rotor, and four capacitive distance sensors fixed to the stator are utilized to implement a resolver. This provides a measure of the rotor orientation that is insensitive to runout of the rotor. A prototype of this design was constructed and tested in the lab to investigate the effect of runout in the tapered rollers and assess the performance of the rim bearing and various resolver designs. We present the results of this testing.

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.