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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1973

Luminous efficiency measurements for silicon and aluminum simulated micrometeors

Laboratory measurements on simulated silicon and aluminum micrometeors in an air atmosphere have produced values for the elemental photographic luminous efficiencies of silicon over a velocity range 13-48 km/sec and of aluminum over a range 12-42 km/sec. The photographic luminous efficiency of both elements first increases with increasing velocity, then reaches a peak and declines. Supplementary measurements on Si and Al in atmospheres of O2 and N2 support the air results.

Becker, D. G.↗

NASA NTRS1975

Luminous stars in galactic supernova remnants

It is shown that luminous stars should be expected in the vicinity of supernova remnants. Luminous stars within the maximum optical areas of supernova remnants are tabulated from catalogs, and an excitation parameter is correlated with the spectral classification of such stars when their UV flux excites H II regions to produce nebular thermal bremsstrahlung. The correlations indicate that the presence of a ZAMS star of type 08 to 05 is necessary to produce thermal bremsstrahlung equal to the observed flux density at 1 GHz. Optical components of seven other supernova remnants are discussed, and it is concluded that gross uncertainties in the distance moduli of both stars and supernova remnants prevent any associations from being made.

Johnson, H. M.↗

NASA NTRS1976

A new interpretation of luminous blue stars

A major revision of current theoretical ideas about the brightest blue stars must be made if Carson's (1976) radiative opacities are adopted in stellar models. Unlike earlier opacities, these exhibit a large 'bump' due to CNO ionization, which leads to very strong central condensation, convective instability, and pulsational instability in hot diffuse stellar envelopes. Despite a number of theoretical uncertainties, the new picture of the structure of very luminous stars is reasonably successful in accounting for a variety of previously unexplained observations. The stellar models for the phase of core hydrogen burning predict large radii and rather cool effective temperatures for O stars and a spreading out of the main-sequence band in the H-R diagram toward luminous cool supergiants for masses higher than about 20 solar masses. In massive X-ray binary systems, circular orbits and supergiant-like visual companions are expected to be quite common. Long-period variability is predicted to exist for massive blue supergiants of luminosity class Ia. The models for helium stars predict large radii and rather cool effective temperatures for Wolf-Rayet stars, as well as multimodal pulsational instability and, possibly, surface turbulence for these stars.

Stothers, R.↗

NASA NTRS1987

Morphology of luminous IRAS galaxies: Summary talk

The author discusses the morphology of luminous Infrared Astronomy Satellite (IRAS) galaxies. A few comments are made about the direction to be taken in future observations of luminous IRAS galaxies.

Becklin, E. E.↗

NASA NTRS1988

Infrared spectroscopy of radio-luminous OH/IR stars

Low-resolution 1.5-2.5-micron spectra for 21 radio-luminous OH/IR stars are presented. These spectra divide into two broad classes. Those with very strong water-vapor absorption closely resemble the spectra of classical Mira variables and are classified Type VM. Those with weaker water-vapor absorption, but still showing strong CO absorption, resemble the spectra of true core-burning supergiants and are classified Type SG. Comparison of the classification of 30 radio-luminous OH/IR stars with their Delta(V)s and luminosities suggests this classification is a good indicator of the intrinsic nature of the underlying star. There is some evidence, however, that some true supergiants (massive main-sequence progenitors) develop the pulsation properties and photospheric characteristics of the Mira-like OH/IR stars when they become optically obscured OH/IR stars.

Jones, Terry Jay↗

NASA NTRS1988

21 centimeter survey of luminous infrared galaxies

This paper presents the results from a 21-cm Arecibo survey of the atomic hydrogen and radio continuum in the most luminous IRAS galaxies of the local universe. Ninety-two galaxies with FIR luminosities in the range of L(FIR) between the solar luminosity values of 2 x 10 to the 10th and 2 x 10 to the 12th were surveyed. Eighty eight of these were detected in the 21 cm line of atomic hydrogen; the radio continuum flux was determined for 80 galaxies. The data of this survey are compared the FIR and optical-wavelength band results. It is noted that luminous IR galaxies show a striking statistical trend for the optical radial velocities to be smaller than the systemic velocities derived from the 21 H I profiles.

Mirabel, I. F.↗

NASA NTRS1989

The ratio of molecular to atomic gas in infrared luminous galaxies

In infrared luminous galaxies the ratio of the CO(1 - 0) to H I integrated fluxes increases with the far-infrared excess, f(fir)/f(b). All infrared active galaxies with f(fir)/f(b) greater than 2 have molecular to atomic gas mass fractions greater than 0.5. Among the galaxies with the higher infrared excesses there are systems with strikingly small atomic mass fractions, where less than 15 percent of the total mass of interstellar gas is in atomic form. The optical morphology of luminous infrared galaxies indicates that the majority, if not all, of these objects are interacting systems. These observations suggest that the overall mass fraction of molecular to atomic gas, and the infrared luminosities per nucleon of interstellar gas are enhanced during galaxy-galaxy interactions.

Mirabel, I. F.↗

NASA NTRS1990

WRA 751, a candidate for a new luminous blue variable

Results are presened on spectroscopic observations (carried out with the ESO 1.52-m telescope at La Silla, Chile) and measurements made by the Infrared Astronomical Satellite on the star WRA 751. It is estimated that the T(eff) of this star is 30,000 K and its E(B-V) is 1.8 mag. Comparison with evolutionary tracks of Maeder and Meynet (1980) indicates that WRA 751 is located in the region of luminous blue variables at a lower limit of the initial mass of about 50 solar masses. Its other physical characteristics, such as the light variability, strong Fe II lines, and the extinction-free spectral energy distribution, suggest that WRA 751 is a candidate for a new luminous blue variable.

Hu, J. Y.↗

NASA NTRS1991

Evolution of luminous IRAS sources - CCD imaging

The paper presents optical imaging of a sample of 64 luminous IRAS galaxies which cover a wide range of IRAS spectra and luminosity and also include a range of optical types. The objects are almost all in current or recent tidal interaction. The connections between the strength and age of the interaction, the IR spectrum and luminosity, and the optical colors, and other properties of the galaxies are discussed. The principal result is that the powerful IR sources with steep IR spectra are stronger and dynamically younger interacting systems, while the flat IR spectrum objects are older. Star formation, dust obscuration, and the timescales for nuclear activity compared with IR and tidal events are discussed, and a self-consistent evolution scenario connecting the luminous IR sources is described.

Hutchings, J. B.↗

NASA NTRS1990

Nearby luminous blue galaxies

Some galaxies are comparable to spirals in terms of blue luminosities but show optical evidence (blue colors, strong emission lines) for large population I stellar components. These luminous blue galaxies provide examples of rapidly evolving large galaxies in the nearby universe. This paper discusses the evolutionary status of luminous blue galaxies and their possible relationships to the excess numbers of faint blue galaxies that are being found by deep surveys of galaxies.

Gallagher, John S., III↗

NASA NTRS1992

Evolution of luminous IRAS sources - Radio imaging

Observations of the compact radio morphology of 111 luminous IRAS-selected active galaxies covering a wide range of IR and optical properties are presented and discussed. Of these sources, 72 are observed for the first time with the VLA A configuration. The circumnuclear radio sources are generally small and weak, with 15 nondetections to a limit of about 0.4 mJy. Comparison with the IR and optical properties of the objects indicates that the radio sources turn on within 10 exp 8 yr of the tidal encounter that is presumed to generate the IR activity. However, the radio sources do not all appear at the same time. The radio observations are consistent with the evolution scenario for luminous IRAS galaxies suggested by Hutchings and Neff (1991).

Neff, S. G.↗

NASA NTRS1992

Color matrix display simulation based upon luminance and chromatic contrast sensitivity of early vision

This paper describes the design and operation of a new simulation model for color matrix display development. It models the physical structure, the signal processing, and the visual perception of static displays, to allow optimization of display design parameters through image quality measures. The model is simple, implemented in the Mathematica computer language, and highly modular. Signal processing modules operate on the original image. The hardware modules describe backlights and filters, the pixel shape, and the tiling of the pixels over the display. Small regions of the displayed image can be visualized on a CRT. Visual perception modules assume static foveal images. The image is converted into cone catches and then into luminance, red-green, and blue-yellow images. A Haar transform pyramid separates the three images into spatial frequency and direction-specific channels. The channels are scaled by weights taken from human contrast sensitivity measurements of chromatic and luminance mechanisms at similar frequencies and orientations. Each channel provides a detectability measure. These measures allow the comparison of images displayed on prospective devices and, by that, the optimization of display designs.

Martin, Russel A.↗

NASA NTRS1993

The starburst-AGN connection - A sensitive VLBI survey of luminous IRAS galaxies

Results of an 18 cm VLBI survey of 31 luminous, radio-compact IR galaxies are presented. Over half the sample galaxies show high-brightness temperature emission, with T sub b greater than 10 exp 5 K and structure on scales of 5-150 mas. The limits for nondetected sources are similar, consistent with a picture in which most of these galaxies have compact cores at a level of a few percent of the total radio flux density. Characteristics of the extended radio structure, infrared properties, and optical excitation are not good indicators of the detectability of VLBI-scale emission. Structural information and energetic considerations rule out a single supernova interpretation of the compact emission in these galaxies, although we cannot exclude the possibility of several simultaneous extraordinarily luminous radio supernovae within the central few hundred cubic parsec. Our results instead favor the presence of an AGN obscured by starburst-related dust.

Lonsdale, Colin J.↗

NASA NTRS1994

Tracking Steady Light Sources Amid Luminous Transients

The Transient Event Rejection for Acquisition and Tracking (TERAT) algorithm governs operation of image-data-acquisition and -processing system. TERAT processes digitized image data to acquire (that is, identify) candidate steady source of light, validate candidate source, and track validated source, all in presence of real or apparent luminous transients represented in image data. Source of light tracked could be star or distant luminous beacon. Transients caused by impacts of ionizing radiation on imaging array of photodetectors or by unsteady light sources not meant to be tracked. TERAT functions with limited data-processing resources. TERAT algorithm currently operational on NASA's TOPEX mission.

Kissh, Frank↗

NASA NTRS1993

Pairing statistics for infrared-luminous galaxies

A knowledge of the pairing fraction of IR-selected galaxies is important in understanding the role of interactions in star formation and nuclear activity. It is clear that interactions are extremely common among the most IR-luminous systems, but results have been inconsistent for less luminous systems; this may result from using peculiar morphology as an indicator of an interaction. Since features associated with milder interactions (e.g., tidal tails) tend to be faint, their detection necessarily depends on the depth of the survey used to identify interacting pairs. We present a sample of IR- and optically-selected galaxies for which we have computed pairing fractions using strictly geometrical, quantitative criteria. For the analysis we used a likelihood ratio technique developed by Keel and van Soest (1992). We find that the pairing fraction for IR-selected galaxies is roughly 30 percent, comparable to that found by Keel and van Soest for optically-selected starbursts. We also detect a strong correlation (r above 0.99) between the 60 micron luminosity of a galaxy sample and its pairing fraction. We conclude that although tidal interactions do not guarantee enhanced activity (AGN or starburst), they can amplify internal properties that would feed such activity.

Gallimore, J. F.↗

NASA NTRS1994

Characteristics of luminous structures in the stratosphere above thunderstorms as imaged by low-light video

An experiment was conducted in which an image-intensified, low-light video camera systematically monitored the stratosphere above distant (100-800 km) mesoscale convective systems over the high plains of the central U.S. for 21 nights between 6 July and 27 August 1993. Complex, luminous structures were observed above large thunderstorm clusters on eleven nights, with one storm system (7 July 1993) yielding 248 events in 410 minutes. Their duration ranged from 33 to 283 ms, with an average of 98 ms. The luminous structures, generally not visible to the naked, dark-adapted eye, exhibited on video a wide variety of brightness levels and shapes including streaks, aurora-like curtains, smudges, fountains and jets. The structures were often more than 10 km wide and their upper portions extended to above 50 km msl.

Lyons, Walter A.↗

NASA NTRS1994

The broad band X-ray spectrum of SN 1978k and two other luminous X-ray sources in the spiral galaxy NGC 1313

We present preliminary results of our analysis of the Advanced Satellite for Cosmology and Astrophysics (ASCA) PV phase observation of the nearby spiral galaxy NGC 1313. ASCA cleanly resolves the three previously known luminous sources, one of which is the very luminous supernova, SN 1978k. The spectrum of SN 1978k is described by either a power law with a photon index gamma approximately 2.2 or a thermal model with temperature kT approximately 3.0 keV and abundances Z approximately 0.2 Z(sun). There is no evidence for strong line emission from it or from the other two sources. The spectrum of SN 1978k arises either in shocked gas in extreme departure from ionization equilibrium or from synchrotron processes associated with a newborn pulsar. A second source, near the galactic center, is well-fit by a power-law with a photon index of approximately 1.8. It is possibly an active nucleus-like source, but physically displaced from the optical nucleus of the galaxy. The spectrum of the third source, located 8 kpc south of the nucleus, along with the absence of an optical counterpart, suggests that it is a low mass X-ray binary; but its high X-ray luminosity clouds this interpretation. This observation demonstrates the ability of ASCA to perform effective broad band spectroscopic measurements of sources at a 2-10 keV flux level of 5 x 10(exp -13) erg cm(exp -2) s(exp -1).

Petre, Robert↗

NASA NTRS1995

ROSAT observations of the luminous X-ray sources in M51

Our analysis of a 24 ks ROSAT Position Sensitive Proprtional Counter (PSPC) image of the interacting galaxies NGC 5194 (M51) and NGC 5195 shows that X-ray emission is distributed across the whole of NGC 5194. In addition to the diffuse emission and a bright nuclear region, eight individual sources were detected with 0.2-2.2 keV luminosities from 5 to 29 x 10(exp 38) ergs/s, more than 10 times higher than typical bright Galactic X-ray sources. The energy distribution of the luminous sources can be characterized by bremsstrahlung spectra with temperatures around 1 keV and low-energy absorption exceeding that expected from our Galaxy. Two sources lie in an inner spiral arm, while five lie along the outer edges of the outer spiral arms. Four sources (R1, R2, R4, R6) lie in or near regions of recent star formation as indicated by H II regions or CO emission from molecular clouds. However, for three of the X-ray sources which fall on the outer edge of the spiral arms (R3, R7, and R8), there is little or no associated CO or H alpha emission. We discuss the origin of the luminous X-ray sources as possibly arising from either massive black holes in binary star systems, supernova remnants, or hot gas associated with star forming regions.

Marston, A. P.↗