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NASA NTRS1988

Extremely luminous far-infrared colliding galaxies - Computation of colliding-galaxy luminosity function

A computational model used to determine the luminosity function for gaseous galaxies in collision is described. It is based on the assumption of high-velocity encounters of two thin, gas-rich disks having identical radii and thickness, able to approach each other from arbitrary directions, with arbitrary orientations and with arbitrary degree of overlap. The distribution of expected luminosities generated in the dissipation of translational energy is then found to closely fit the observed distribution of luminosities of extremely luminous IRAS galaxies. Bursts of star formation resulting from such collisions would not have the correct luminosity function.

Harwit, Martin↗

NASA NTRS1988

High spectral resolution observations of HD 44179 at 3.2-3.7 microns

New high-resolution spectra of HD 44179 (the 'Red rectangle') in the 3.2-3.7 micron range are presented. Contrary to previous observations, no evidence is found for the 3.4 micron feature which is supposed to arise from aromatic hydrocarbons. The strong 3.29 micron feature is found to be different from that seen in NGC 7027 and IRAS 21282+5050.

Tokunaga, A. T.↗

NASA NTRS1987

The Large Deployable Reflector (LDR) - Plans and progress

The program history, scientific aims, design, and projected performance of the LDR, a 20-m-primary two-stage four-mirror orbiting sub-mm/FIR astronomical observatory under NASA development, are reviewed. It is shown that the LDR would provide capabilities complementary to those of IRAS, the Kuiper Airborne Observatory, the IRTF, the Hubble Space Telescope, and the planned Space IR Telescope Facility for observations of small-scale background anisotropies, high-redshift galaxies, and objects at temperatures of a few times 10 K or lower. The current design concept is illustrated with extensive drawings, diagrams, and tables of instrument parameters. Particular attention is given to the graphite-epoxy facing and Al-honeycomb core of the primary structure, the focal-plane instruments, and outstanding technological problems.

Swanson, Paul N.↗

NASA NTRS1987

Infrared observations of Be stars

IRAS observations of the Be stars and the correlations between the IR excess and the stellar parameters are discussed. The quantitative interpretation of the IR excess is described and interpreted in terms of the characteristics of the circumstellar material. Some of the major problems of the IR studies of Be stars are examined, and possible future studies are addressed.

Lamers, Henny J. G. L. M.↗

NASA NTRS1988

Powerful warm infrared sources in early-type galaxies

IRAS far-infrared sources have been identified with 129 S0, Sa, Sb, and Sc galaxies in a statistically complete sample of 738 galaxies brighter than 14.5 mag and smaller than 4.0 arcmin. In most cases, the far-IR colors and the ratios of far-IR flux to radio flux density are those of normal galactic disks and/or starbursts. The most powerful far-IR sources in S0 and Sa galaxies are just as powerful as the strongest far-IR sources in Sb and Sc galaxies. Bright-IR sources in S0 and Sa galaxies are warm; those in Sc galaxies are cool. Sb galaxies have both warm and cool IR sources. Bright warm IR sources occur much more frequently in barred galaxies than in galaxies without bars for types S0, Sa, and Sb. Bright, cool IR sources are found with increasing frequency along the Hubble sequence, regardless of the presence or absence of a bar. At least some 'S0' galaxies with warm, bright IR sources have peculiar morphologies and ambiguous classifications.

Dressel, L. L.↗

NASA NTRS1988

Vaporization of ices containing S2 - Implications for comets

An effort is made to ascertain whether the S2 detected in Comet IRAS-Araki-Alcock 1983d can be stored in ices during warming, and is released during the vaporization of its water ice matrix, in view of data on the UV spectrum of S2 in Ar and Kr matrices and water ice in which the ratio of matrix or molecular ice to S2 is of the order of 500:1. The results obtained support the hypothesis that the S2:H2O ratio in the solid phase may not be a predictor of the gas phase ratio. It is concluded that similar vaporization from a cometary nucleus would not release most of the S2 contained in the ice.

Moore, M. H.↗

NASA NTRS1988

X-ray sources in regions of star formation. III - Naked T Tauri stars associated with the Taurus-Auriga complex

Ground-based and IRAS optical and IR spectroscopic and photometric observations are reported for 90 stars in or near 59 Einstein Observatory X-ray error circles in the Tau-Aur region. The data are presented in extensive tables and sample spectra and characterized in detail, with particular attention to 28 newly discovered 'naked' T Tau stars, which are shown to be normal stars with no significant IR or UV excess and ages of 1-40 Myr. These stars are found to outnumber normal T Tau stars by a factor of 10 in an area near the Tau-Aur dark clouds, and it is argued that their evolution toward the ZAMS is typical for low-mass stars. The implications of this finding for the time scales of circumstellar-disk dissipation and planet formation are discussed.

Walter, Frederick M.↗

NASA NTRS1988

Far-infrared emission in single and binary galaxies

The properties of the far-IR emission from a sample of optically selected isolated galaxies is studied using data obtained by the Infrared Astronomical Satellite (IRAS). This set of galaxies is used as a standard of comparison representing galaxies whose far-IR properties have been little influenced by interaction with their surroundings. An optically selected sample of isolated binary galaxies is then considered. For the binary galaxies, no extreme highly luminous IR emitters are found, reaffirming the rarity of these objects. However, the occurrence of some low-level enhancement of infrared activity is substantiated by the comparison of far-IR emission in single galaxies and those found to have nearby companions. This effect may be influenced by the occurrence of a few instances of more luminous galaxies. Indeed, many galaxies that show evidence for interaction, i.e., distortion, tails, etc., do not show enhanced IR emission.

Haynes, Martha P.↗

NASA NTRS1988

Spectra of galaxies in the Case Low-Dispersion Sky Survey in the direction of the Bootes void

A sample of 34 galaxies selected from the Case Low-Dispersion Northern Sky Survey in the direction of the Bootes void. Emission-line redshifts were obtained for 33 objects; the spectrum of the thirty-fourth galaxy contains no obvious features. Three of the emission-line galaxies are lcoated within the boundaries of the Bootes void, including one not previously reported. To date, all the galaxies discovered in the void have emission-line spectra. Although more than half the galaxies in the sample are fainter than M(B) = -21.0 mag, all five of the galaxies that were detected by IRAS are brighter than M(B) = 21.5 mag. The relative strengths of the emission lines in most of the galaxies, including those in the void, indicate the lines are excited by photoionization due to young, hot O and B stars. Possible causes for the star formation occurring in these galaxies include interaction with nearby galaxies, star formation induced by nuclear activity, and/or recent development of physical conditions required for star formation.

Weistrop, Donna↗

NASA NTRS1988

Interaction between high-velocity pulsar in CTB80 and an infrared emission shell

During a survey of infrared emission detected by IRAS from shock-heated dust associated with Galactic SNRs, a roughly 1 deg diameter supernova remnant shell centered 30 arcmin east of SNR CTB80's core was discovered. The pulsar's projected location inside this infrared emission shell, together with similar distance and age estimates, suggest that both the shell and pulsar were produced by the same supernova event. It is proposed that the interaction between the pulsar's energetic particle emission and the shell's compressed interstellar magnetic field can explain CTB80's remarkable radio structure, and the implications of such pulsar/SNR interactions are discussed.

Fesen, Robert A.↗

NASA NTRS1988

Resonance fluorescence calculations for some sulphur diatomics in comets

Statistical equilibrium calculations have been carried out for S2 which was detected in Comet IRAS-Araki-Alcock and for SO, SH and CS+ which are likely to be present in the cometary comas. In all cases, a pattern of features of similar intensity is predicted - so that identifications are possible even when signal : noise is poor and other emissions interfere. These results can guide searches and help confirm the presence of these features in cometary spectra.

Krishna Swamy, K. S.↗

NASA NTRS1988

Infrared brightness of a comet belt beyond Neptune

The infrared brightness of a flattened comet belt beyond the orbit of Neptune is considered using a disk-like model with a power-law density distribution of comets. This spectrum is compared with the emission from a model zodiacal dust cloud in the ecliptic and with published IRAS data and some consequences of dust in the comet belt are presented.

Jackson, A. A.↗

NASA NTRS1987

Sub-mJy radio sources - A population of starburst galaxies at intermediate redshifts

Optical-infrared observations are used to show that the sub-mJy sources, discovered in deep radio surveys and responsible for the upturn in the radio source counts at sub-mJy levels, represent a population of star-forming galaxies at intermediate redshifts and with Mv between about -23 and -20. The very high frequency of line-emission, the very large incidence of galaxy mergers and interactions associated with these sub-mJy sources, and the good agreement between the sub-mJy radio source counts and the counts of starburst galaxies from deep IRAS surveys imply that these star-forming galaxies are in fact undergoing starbursts.

Thuan, Trinh X.↗

NASA NTRS1988

On the redistribution of OB star luminosity and the warming of nearby molecular clouds

IRAS observations of the neighborhoods of six H II regions in the outer Galaxy are correlated with CO maps of the same regions. It is found that more than half of the far-IR luminosity from within about 25 to 75 pc of the ionizing stars is contributed by dust associated with molecular clouds. It is shown that a major and increasing fraction of the OB cluster starlight is not absorbed locally. The observations suggest that the H II regions are not radiation-bounded and have ion densities of about 1/cu cm. A model describing the interstellar environment of OB star clusters as a function of time is presented.

Leisawitz, D.↗

NASA NTRS1988

Infrared limb brightening in the Barnard 5 cloud

IRAS and (C-13)O data are presented for the dark cloud Barnard 5. The 100-micron and (C-13)O emission are well correlated and suggest that the 100-micron emission traces the dust and gas column density through the cloud. The 12-micron emission, on the other hand, is anticorrelated with the overall opacity in the cloud, which is interpreted as limb brightening in the context of a model in which small dust grains, probably PAHs, are transiently excited by the absorption of UV photons in a thin shell around the denser parts of the cloud.

Beichman, C. A.↗

NASA NTRS1988

The galatic and LMC extreme line supergiants compared: IUE observations of the Henize-Carlson and Zoo star samples of massive supergiants

The Henize-Carlson sample of galactic massive supergiants, and a comparison between the Galactic and LMC samples are discussed. Several of the stars, notably He3-395 and S 127/LMC, have very similar shell characteristics. There appears to be little difference, other than luminosity, between the LMC and Galactic samples. One star, He3-1482, was detected with the Very Large Array at 6 cm. The UV data is combined with IRAS and optical information.

Shore, S. N.↗

NASA NTRS1988

Research in planetary astronomy

The objective is the continuation of a long-term research program designed to study the composition, structure and processes operating on the surfaces of solar system objects using the Mauna Kea Observatory with techniques and modern instrumentation. Reflectance spectroscopy and multispectral imaging in the spectral region, 0.3 to 5.0 micrometer are the major techniques used, although thermal (10 micrometer and 20 micrometer) radiometry are used in some aspects of the research. Some specific projects include: (1) systematic spectral imaging observations of the Moon; (2) systematic spectral imaging and spectral monitoring of the Martian surface; (3) thermal radiometry of asteroids as part of the IRAS follow-up and other target specific programs; (4) searches for asteroid satellites and dust belts using a stellar coronagraph; and (5) studies of circumstellar disks using a stellar coronagraph. Progress for each of the programs included is discussed. minerals; (2) completed observations of lunar multi-ringed basins and crater deposits in search of high-Ca spectral anomalies; (3) completed data reduction of an additional 5 asteroids observed by the coronagraphic technique in the search for asteroids satellites and debris clouds; and (4) completed the reduction and calibration of 350 asteroids observed at 10 micron and 20 micron using the NASA IRTF.

Mccord, Thomas B.↗

NASA NTRS1988

Physical properties of asteroids

Infrared photometry at 1.2, 1.6 and 2.2 micrometer provides a relatively rapid and accurate method for the classification of asteroids and is important for comparison with laboratory measurements of meteorites and other possible compositional analogues. Extension beyond the visual is espicially useful for minerals which have strong characteristic infrared colors such as olivine in the A class asteroids. Radiometry at long infrared wavelengths is important for deriving basic physical parameters (via thermal models) such as size and albedo which in turn enables the conversion of relative colors to absolute reflectances. In particular, albedos are the only way to distinguish among the otherwise ambiguous E, M and P classes of asteroids. Infrared observations of 15 asteroids were made at the NASA infrared Telescope Facility (IRTF) on Mauna Kea in 1987. Researchers completed the analysis of 22 Aten, Apollo and Amor asteroids. Results include albedos and diameters for these objects as well as the identification of the first known class M and Class E near-Earth asteroids. The standard thermal model appears to be inadequate for some of these small asteroids because of their coarse regolith, so researchers constructed a rotating thermal model for such asteroids. They have identified a subtle systematic difference between the sub-populations of large and small IRAS asteroids as well as several anomalous objects.

Veeder, Glenn J.↗