Douglas W. Toomey

Design for a 1--5-um cryogenic echelle spectrograph for the NASA IRTF

The design of an infrared cryogenic echelle spectrograph for use on the NASA Infrared Telescope Facility is described. The resolving power achieved over the range 1-5.4 microns is 1-40,000 with slit widths of 2.0-0.5 arcsec. The spectrograph is used in a single order with a 30-arcsec-long slit. No cross dispersion is provided because of the small number of orders that can be observed at once and the need to keep the instrument as small as possible. A closed-cycle cooler is used in lieu of cryogens in order to achieve greater reliability and ease of use at the telescope. The optical layout, the design philosophy, the modes of operation, and the construction details are provided.

SpeX: a medium-resolution IR spectrograph for IRTF

SpeX is a medium-resolution 0.8-5.5 micrometers cryogenic spectrograph being built at the Institute for Astronomy, University of Hawaii, for the NASA IR Telescope Facility on Mauna Kea. SpeX was funded by the National Science Foundation in July 1994. First-light is expected in 1999. The primary scientific driver of the instrument is to provide maximum simultaneous wavelength coverage at a spectral resolving power which is well-matched to many planetary, stellar and galactic features, and which adequately separates sky emission lines and disperses sky spectral resolutions of R approximately 1000-2000 simultaneously across 0.9-2.5 micrometers , 2.0-4.2 micrometers , or 2.4- 5.5 micrometers . SpeX will use an Aladdin II 1024 X 1024 InSb array in its spectrograph and an Aladdin II 512 X 512 InSb array in its IR slit-viewer.

A Redetermination of the Mass of Procyon

The parallax and astrometric orbit of Procyon have been redetermined from PDS measurements of over 250 photographic plates spanning 83 years, with roughly 600 exposures used in the solution. These data are combined with two modern measurements of the primary–white dwarf separation, one utilizing a ground-based coronagraph, the other, the Planetary Camera (PC) of the Hubble Space Telescope. Together with the redetermined astrometric orbit and parallax, these yield new estimates of the component masses. The derived masses are 1.497 ± 0.037 M⊙ for the primary and 0.602 ± 0.015M⊙ for the white dwarf secondary. These mass values are heavily weighted by the PC separation measurement, which, while being somewhat discordant with the ground-based measures, we argue is more precise and more accurate and thus deserving of its greater weight. This stated, the long-standing discrepancy between previous determinations of the observed mass of Procyon A (1.75 M⊙) and the value supported by stellar evolution models (1.50 M⊙) appears to be reconciled.

Design of a new 1-5.5-μm infrared camera for the NASA Infrared Telescope Facility

The design of a multipurpose 1 - 5.5 micrometers infrared camera (NSFCAM) for the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, is described. The camera is built around the new 256 X 256 InSb array manufactured by Santa Barbara Research Center (SBRC) and incorporates a variety of observing modes to fulfill its role as a major facility instrument. These include three remotely-selectable image scales, a selection of fixed bandpass filters, R equals 50 - 100 spectral resolution circularly variable filters, a grism, coronographic masks, and a polarization imaging capability. Through the use of flexible array clocking schemes, driven by programmable digital signal processors (DSPs), we plan to implement several new operating modes, including real-time shift and add for image stabilization, and fast subarray readouts for occultations. Simultaneous optical and infrared imaging of the same field will be possible through the use of a cold dichroic beamsplitter. This feature is primarily intended for use with the IRTF tip-tilt image stabilization system currently being built. Given a suitable guide star, the camera should achieve near-diffraction limited imaging at 2 - 5 micrometers . In this paper we discuss the design of the optics, cryogenic, electronics and software needed to provide the camera with these capabilities.

CoCo: an experiment in infrared coronagraphy at the IRTF

Imaging planets, brown dwarfs and disks around nearby stars is a challenging endeavor due to the required scene contrast. Success requires imaging down to m equals 20-25 within arcseconds of stars that are 4th-6th magnitude. Light scattered and diffracted from a variety of sources increases the background flux in the area of interest by orders of magnitude masking the target objects. As first shown by M. B. Lyot in 1939 masks can be placed in the focal pane and pupil planes of a camera to occult the bright central source making it possible to image the faint extensions around it. CoCo is an experiment in using a coronagraphic camera, for IR observations, on a large telescope in an effort to understand how a coronagraph can help and how to properly design one of the new generation of large telescopes. Recent result with CoCo show a factor of 5-10 reduction in background levels in the area from 2-7 arcseconds from the central object. This paper will describe those result and summarize what has been learned towards building coronagraphic cameras for todays large telescopes.

ProtoCAM: an innovative IR camera for astronomy

ProtoCAM, a new infrared array camera, has been built for the NASA 3-m Infrared Telescope Facility (IRTF). The camera is built around a 62 x 58 InSb hybrid array and is sensitive throughout the 1-5-micron atmospheric windows. The camera is equipped with standard astronomical filters as well as a full complement of continuously variable filters providing a spectral resolution down to 1 percent. On the IRTF, the platescale is variable real-time from 0.14 to 0.35 arcsec. The camera, the electronics, the software, and the performances are discussed, and some preliminary astronomical results are presented.

Redline multiple-array controller for SpeX

The NASA IRTF is building a multiple digital signal processor (DSP) based array electronics control system for SpeX, an NSF funded 1 to 5 micron medium resolution spectrograph. SpeX will use a 1024 X 1024 InSb array for spectroscopy and one 512 X 512 quadrant of another 1024 X 1024 InSb array for slit field viewing and IR guiding. An additional system is also being produce at the Institute for Astronomy for the SUBARU IR camera and spectrograph (IRCS). Plans for IRCS include the use of a 1024 X 1024 InSb array for spectroscopy and one 1024 X 1024 InSb array for IR imaging. This document will provide the instrument derived requirements, an overall system description, and some of the tradeoffs and technical choices made. The design for both system is an evolutionary upgrade of the current IRTF array control electronics system used in a 256 X 256 InSb based imager, a 256 X 256 InSb and 512 X 512 CCD in an echelle spectrograph, an 800 X 800 CCD based tiptilt correction system and a non-IRTF 128 X 128 Si:As BIB array based imager.

MOP: an infrared multichannel occultation photometer for planetary astronomy

The design of a multichannel occultation photometer built under NASA contract to SETS Technology, Inc., for the NASA 3-m IR telescope facility (IRTF) and the JPL Table Mountain telescope is described. This instrument acquires data in four selectable passbands (two 1 to 5 micrometers channels and two 10 to 20 micrometers channels), with very high sensitivity and approximately 100% duty cycle on-source during chopping. The optics are optimized for uniform response across an aperture of up to 20 arcseconds on the IRTF. The cryogenic system is a two-can cryostat with one liquid nitrogen can for cooling the radiation shields, optics, filters, and baffles, and a liquid helium can for cooling the IR detectors. The instrument operates two types of IR detector technologies. The 1 to 5 micrometers detectors are low-capacitance, single-element InSb detectors. The 10 micrometers detectors are blocked impurity band detectors. The instrument also has a 64 by 64 visible CCD array as an additional channel for guiding and visible photometry. A global positioning system unit is incorporated into the system for time and location stamping of occultation events. The instrument design and construction are discussed.