Tony T. Young

IRCS : Infrared Camera and Spectrograph for the Subaru Telescope

A 1-5 micrometers IR camera and spectrograph (IRCS) is described. The IRCS will be a facility instrument for the 8.2 m Subaru Telescope at Mauna Kea. It consists of two sections, a spectrograph and a camera section. The spectrograph is a cross-dispersed echelle that will provide a resolving power of 20,000 with a slit width of 0.15 arcsec and two-pixel sampling. The camera section serves as a slit viewer and as a camera with two pixel scales, 0.022 arcsec/pixel and 0.060 arcsec/pixel. Grisms providing 400-1400 resolving power will be available. Each section will utilize an ALADDIN II 1024 X 1024 InSb array. The instrument specifications are optimized for 2.2 micrometers using the adaptive optics and the tip-tilt secondary systems of the Subaru Telescope.

KSPEC -- A NEAR-INFRARED CROSS-DISPERSED SPECTROGRAPH

KSPEC (K-Band Spectrograph) is an infrared spectrograph designed primarily for spectroscopy in the 2.0 - 2.5 micron region. It offers two different optical configurations. The first is a cross-dispersed echelle mode designed to cover the atmospheric windows from 1 - 2.5 microns in one spectral frame of 256 X 256 format on a NICMOS-3 HgCdTe detector array. This configuration of the spectrograph provides medium spectral resolution (lambda/delta-lambda ~500) for spectral classification work, emission-line detection, and redshift measurements. Alternatively, KSPEC can be equipped with a different spectrograph camera, giving a long-slit, single-order spectrum from 2.05 - 2.35 microns. The instrument uses a second NICMOS-3 infrared detector array for slit-viewing, to facilitate the acquisition of optically invisible objects, to document the slit position and to monitorit during long spectroscopic integrations. KSPEC does not contain any moving components, making it a very reliable, relatively low-cost instrument that is easy to use.

Gemini near-infrared imager (NIRI)

The NIRI for the Gemini North telescope is now undergoing acceptance testing. NIRI is the main near-IR facility camera on the Gemini North telescope and is designed to fully exploit the excellent characteristics of the site and the expected high performance o the telescope. NIRI offers 3 different pixel scales for wide-field, tip-tilt corrected and diffraction-limited imaging. It is equipped with a pupil imaging system to evaluate the telescope emissivity and to optimize the alignment of the instrument with the telescope. NIRI has an IR wavefront sensor so that tip-tilt and focus corrections can be obtained even in dark cloud regions or during daytime observing.

Gemini near-infrared imager

We discuss the main design features of the Gemini Near-IR Imager (NIRI) and its scientific capabilities. NIRI is designed to fully exploit the excellent image quality and low telescope emissivity expected from the Gemini telescope on Mauna Kea. It offers a range of pixel scales matched to different scientific objectives and has spectroscopic as well as polarimetric capabilities. One of its main design features is the use of a near-IR 2 X 2 Shack-Hartmann wavefront sensor for tip-tilt and focus control.

The University of Hawaii 2.2 Meter Fast Tip‐Tilt Secondary System

Using a new f/31 secondary on a tip-tilt platform, we have built an image-stabilization system which has been used regularly for astronomical imaging and spectroscopy on the University of Hawaii 2.2 m telescope. Diffraction-limited cores of stellar point-spread functions are achieved in near-infrared imaging, with Strehl ratios as high as 0.47. K-band images with 03 FWHM resolution (without deconvolution) are routinely obtained. The construction, operation, and capability of the current system are described, a summary of recent scientific findings is presented, and future improvements are outlined.

Design of the near-infrared camera for the Gemini telescope

The Gemini Infrared Imager is a 1 - 5.5 micrometers general purpose camera to be built by the Institute for Astronomy for the Gemini Telescope on Mauna Kea, Hawaii. The camera will provide both high spatial resolution and wide field modes, and support spectroscopic, coronographic, and polarimetric capabilities. The camera project is currently in its preliminary design phase. We present the results of the conceptual design study.

Cryostat mechanism design and fabrication

The harsh operating environment of high vacuum and extremely low temperature poses several challenges to cryogenic mechanisms. These challenges include out-gassing, physical property change of metal and nonmetal materials, differential thermal shrinkage of different materials. Many motorized cryogenic mechanisms have been designed and fabricated for various IR instruments at the Institute for Astronomy. These mechanisms include detector focus stages, filter wheels, 2 and 3-position bema selectors, lens switchers, grating tilt stages and gimbal mirror mounts. Cryogenic motors are used for all these mechanisms. The following topics will be discussed in this paper: motor selection, material selection, stress relieve and surface treatment, ball bearing and ball screw selection and treatment, bushing materials, lubrication methods, flex pivots, and Hall effect sensors.

Design of the cryogenic wheel mechanisms for IRCS and NIRI

The IR camera and spectrograph (IRCS) for SUBARU and Gemini near-IR imager (NIRI) instruments have a common design for all wheels, based on a modified geneva mechanisms with a locking cam actuated detent pin. The geneva design, in combination with the spring loaded detent mechanism, allows the stepper motor/spur gear drive to decouple from the wheel at each aperture position. The detent mechanism positions the wheel precisely. The need for precise motor control and wheel position encoding is reduced because of the detent mechanism. Six of these mechanism are filters wheels requiring repeatable aperture positing. The other seven mechanisms include of a slit wheel, grism wheel, pupil mask wheel, 2 beam steerers, a focal p;lane mask wheel, and a beamsplitter wheel. These mechanisms require repeatable, stable and accurate positioning. The number of aperture positions for the 13 wheels range from 2 to 16. The mechanisms are aligned and tested at room temperature and operated at 60 K, requiring an athermal design, for which the modified geneva mechanism is ideally suited. This paper will discuss the prototype development and final mechanical design of specific wheel mechanisms completed for the IRCS and NIRI instruments at the Institute for Astronomy.

Cryostat design and fabrication for the Gemini NIRI instrument

The Gemini Near IR Imager (NIRI) is a cryogenic instrument cooled by two closed-cycle cryo-coolers. The vacuum jacket is a hexagon shaped vacuum vessel made of three sections. Each section is forged out of aluminum 6061. All the internal structural components are made of aluminum 6061T6 except the supporting trusses, which are made of titanium. All the internal structural members are stress relieved to maintain dimensional stability and good optical alignment. The thermal insulation includes floating shields and cold shields. Two closed-cycle coolers are mounted opposite to each other and electronically synchronized in order to cancel the vibration caused by the oscillating expansion valve. Several different fabrication methods and stress relief methods are discussed.

Design review of flexure focus stage for the Gemini telescope near-infrared imager

Reviewed is a focus stage designed to accommodate the positioning and stability requirements of the detector arrays in the Gemini North Telescopes Near IR imager (NIRI). Focus axis translation of the two detector arrays is required, while sub-micron deflection stiffness about all other axes is of paramount importance to the successful operation of NIRI. The stiffness requirement coupled with a cryogenic vacuum environment led to a flexure design. Testing of the prototype stage mechanism to date has shown transverse deflections of < 1 micrometers , positioning repeatability of 1 micrometers , and satisfactory cryogenic performance.