Showing papers by "George H. Rieke published in 1993"

M dwarf spectra from 0.6 to 1.5 micron - A spectral sequence, model atmosphere fitting, and the temperature scale

Abstract: Red/infrared (0.6-1.5 micron) spectra are presented for a sequence of well-studied M dwarfs ranging from M2 through M9. A variety of temperature-sensitive features useful for spectral classification are identified. Using these features, the spectral data are compared to recent theoretical models, from which a temperature scale is assigned. The red portion of the model spectra provide reasonably good fits for dwarfs earlier than M6. For layer types, the infrared region provides a more reliable fit to the observations. In each case, the wavelength region used includes the broad peak of the energy distribution. For a given spectral type, the derived temperature sequence assigns higher temperatures than have earlier studies - the difference becoming more pronounced at lower luminosities. The positions of M dwarfs on the H-R diagram are, as a result, in closer agreement with theoretical tracks of the lower main sequence.

M82: The saga continues

Abstract: We present new near-infrared observations of the starburst galaxy M82, including high-resolution J, H, and K imagery, 1-5 μm spectrophotometry and photometry, and 1.05-1.35 μm spectroscopy. These measurements are used to examine the stellar population in the galaxy and conditions in the interstellar medium. We combine our observations with results from the literature to derive a new set of constraints for starburst models, which are presented in a companion paper. Our measurements of Paschen line fluxes in combination with the strengths of other recombination lines allow study of the reddening in M82. We find that a uniform foreground screen model for the dust geometry cannot explain the relative line strengths

The Stellar Population in the rho Ophiuchi Cluster

Abstract: We report a near-infrared survey of 200 arcmin 2 in the cores of the ρ Ophiuchi interstellar clouds, leading to the detection of 91 sources. We develop a new method for estimating the luminosities of these sources based on fitting of isochrones from theoretical models. Application of this method allows us to determine a luminosity function and accompanying initial mass function for the cluster of young stars forming in these clouds. The IMF extends to well below the bottom of the main sequence (0.08 M ○. ) with no obvious feature at the transition between stellar and substellar masses. The power-law exponent of the IMF at low stellar and substellar masses is roughly −1.3 to −1.1, with formal errors of 0.2

Compact high-resolution IR spectrometer for the Columbus Telescope

Abstract: An infrared, cryogenically-cooled, grating spectrometer has been designed for the Columbus Project (2 X 8.4-m telescopes) and MMT Conversion (6.5-m). On one barrel of the Columbus Telescope and using a NICMOS3 array of 256 X 256 40 micrometers HgCdTe detectors, the instrument will project each pixel to 0.33 arcsec. With a slit of 0.66 arcsec width (2 pixels), the available spectral resolutions will range from (lambda) /(Delta) (lambda) equals 670 to 19,000. The optics are achromatic from 1.4 to 5 micrometers , allowing use of a variety of array types. The first version of this instrument has been built and fitted with optics that allow its use with the Steward Observatory 1.5-m and 2.3-m telescopes. It is relatively inexpensive ( 3 ). The high spectral resolution in such a compact instrument will be achieved through an echelle grating immersed in silicon. We discuss the processing for producing such gratings, including demonstrations that we have conducted on test blanks. We report on the preliminary performance of the prototype instrument and on unique design features that may be useful for other spectrometers.

IRS 16: The Galaxy's Central Wimp?

Abstract: We have constructed burst models of the stellar population in the Galactic center. Many classes of models can be excluded entirely. Models with an age of 7-8 Myr and an initial mass of less than 4×10 5 M ○. can reproduce the red supergiant stars and stars with the continuum characteristics of IRS 16 and provide the ionizing flux. We show that if IRS 16 is the product of normal stellar evolution associated with a recent star formation burst that currently dominates the energetics of the region, then IRS 16 itself is inconsequential to Galactic center energetics

Ground-based camera experience with NICMOS arrays

Abstract: Several cameras employing NICMOS2 (128 X 128) and NICMOS3 (256 X 256) arrays have been used in diverse applications on ground-based telescopes. Such use of arrays provides many insights to their performance that are not usually obtained in laboratory tests, and provides a baseline of performance over repeated thermal cycles. Astronomical use of these arrays also involves extracting accurate photometric information and detection of sources in spite of high background levels. The NICMOS arrays have proven very capable as astronomical imagers.

High-performance Ge:Ga arrays for the far infrared

Abstract: We report on progress in the construction of highly sensitive arrays of germanium photoconductors for operation at wavelengths between 40 to 120 micrometers . This technology is being developed for future astronomical missions in the far infrared such as SIRTF. We are evaluating construction techniques that will allow us to build 32 X 32 format arrays that are reliable and suitable to be qualified for space flight, while retaining the excellent performance of a prototype we have built and tested previously. We review the technical issues in constructing large format far infrared arrays, along with a description of the approaches that have been adopted in a prototype array to deal with these issues. We report on the development of two advanced methods to interconnect the detectors and readouts, that allow the extension of the Z-plane concept to larger formats: (1) Flex cable and (2) tape automated bonding. Both methods are being evaluated in a detailed series of laboratory experiments, including the electrical performance of the integrated readout/interconnect systems, thermal performance, ease of assembly of completed arrays, and mechanical ruggedness. These approaches will be discussed in terms of their use both with readouts that need to operate at temperatures above those acceptable for the detectors (approximately 20 K) and with readouts that can operate close to the detector temperature (approximately 2 K).

IRS 16: The Galaxy's Central Wimp?

Abstract: We have constructed burst models of the stellar population in the Galactic center. Many classes of models can be excluded entirely. Models with an age of 7-8 Myr and an initial mass of less than 4×10 5 M ○. can reproduce the red supergiant stars and stars with the continuum characteristics of IRS 16 and provide the ionizing flux. We show that if IRS 16 is the product of normal stellar evolution associated with a recent star formation burst that currently dominates the energetics of the region, then IRS 16 itself is inconsequential to Galactic center energetics

SIRTF instrument concepts

Abstract: This paper describes the current design concepts for the three scientific instruments which are under definition study for NASA's Space Infrared Telescope Facility (SIRTF) These instruments, the Infrared Array Camera (IRAC), the Infrared Spectrograph (IRS), and the Multiband Imaging Photometer for SIRTF (MIPS), will provide imaging and spectroscopy from25 to 200 jim Over much of this range their performance will be limited only by natural astrophysical backgrounds in the solar system, and by diffraction Changes in the instrument complement from the former Titan launched, Earth orbiting SIRTF concept to the present Atlas launched, solar orbiting concept are discussed 1 INTRODUCTION The Space Infrared Telescope Facility (SIRTF) will be the first cryogenic infrared space observatory to take full advantageof the extraordinary advances in infrared detector technology over the past decade Young1 describes these advances in this volume SIRTF will use an 85 cm diameter telescope cooled with liquid helium for a minimum of three years to addressastrophysical questions such as the origin of planets, stars, and galaxies, asdiscussed by Werner and Osmolovsky2 The