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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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At least 379 records · Page 21
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NASA NTRS1981

The close multiple system mu Orionis - Masses and the mass-luminosity relation

The observations made of the secondary component B of the close visual binary mu Ori are described. The Reticon observations made at red wavelengths showed the secondary to be a double-lined spectroscopic binary with a period of 4.78 days and nearly identical components having minimum masses of 1.1 solar mass each. Previous estimates are corroborated by the large spectroscopic mass ratio of B to A and B. The discovery that B is a pair of late-F dwarfs solves the apparent mass-luminosity relation discrepancy noted in previous studies.

Fekel, F. C., Jr.↗
NASA NTRS1981

Pulsar gamma-rays - Spectra, luminosities, and efficiencies

The general characteristics of pulsar gamma-ray spectra are presented for a model in which the gamma rays are produced by curvature radiation from energetic particles above the polar cap and attenuated by pair production. It is found that the shape of the spectrum depends on pulsar period, magnetic field strength, and primary particle energy. Comparing numerically calculated spectra with the observed spectra of the Crab and Vela pulsars, it is determined that primary particles must be accelerated to energies of approximately 3 x 10 to the 7th m c-squared. A general formula is determined for pulsar gamma-ray luminosity; it is found to depend on period and field strength.

Harding, A. K.↗
NASA NTRS1981

On the maximum luminosity in X-ray bursts

A qualitative model is proposed which relates the burst behavior of 1608-52 observed by Murakami et al (1980) to the composition of the envelope in which the X-ray bursts occur. The model provides an explanation for the large scatter in the peak fluxes when the accretion rate is high. A flux would be transported outward at the top of the convective region which equals 1.5 to 2 times the Eddington limit appropriate to a helium-rich gas. Upon traversing the outer part of the accreted layer, which is not affected by the nuclear processes and is therefore hydrogen-rich, this flux is about a factor of 3 to 4 higher than the local value of the Eddington luminosity.

Van Paradijs, J.↗
NASA NTRS1981

A new determination of the halo luminosity density of the galaxy

The distribution of tangential velocities for arbitrary halo velocity dispersions and rotation rates are explicitly computed, assuming a particular form of the halo velocity distribution function near the sun. It is found that for a specific model of the halo velocity dispersion tensor that Schmidt's (1975) estimate of the mass carried by halo stars of 0.25-0.70 solar masses should be revised by a factor of between 1.0 and 2.0, depending on the rotation rate of the halo. Although obtaining a mass density in all stars from the stellar density in that mass range is extremely uncertain, it is found, in agreement with earlier work, that even under rather extreme assumptions about the remnants the observed stars and expected remnants fail to provide the theoretically expected mass. Comparison of the luminosity to the theoretical mass yields a mass to light ratio consistent with that of rich clusters of galaxies.

Richstone, D. O.↗
NASA NTRS1981

A complete X-ray sample of the high latitude sky from HEAO-1 A-2: log N lo S and luminosity functions

An experiment was performed in which a complete X-ray survey of the 8.2 steradians of the sky at galactic latitudes where the absolute value of b is 20 deg down to a limiting sensitivity of 3.1 x ten to the minus 11th power ergs/sq cm sec in the 2-10 keV band. Of the 85 detected sources 17 were identified with galactic objects, 61 were identified with extragalactic objects, and 7 remain unidentified. The log N - log S relation for the non-galactic objects is well fit by the Euclidean relationship. The X-ray spectra of these objects were used to construct log N - log S in physical units. The complete sample of identified sources was used to construct X-ray luminosity functions, using the absolute maximum likelihood method, for clusters galaxies and active galactic nuclei.

Piccinotti, G.↗
NASA NTRS1982

Quick matching technique to study the relationship between solar radius and luminosity variations

A simple matching technique is developed which makes it possible to compute the response of the solar envelope to perturbations which occur within the solar convective region in timescales of importance to climate. The technique is applied to perturbation of the convective efficiency (alpha-mechanism) and of the nongas component of the pressure in different regions of the convection zone (beta-mechanism). The results indicate that whereas either perturbation affects the solar luminosity, the alpha-mechanism has almost no effect on the solar outer radius, regardless of the affected region. The beta-mechanism, however, produces radius changes which may be large if the location of perturbation is deep enough.

Sofia, S.↗
NASA NTRS1982

The evolution of solar ultraviolet luminosity

Astronomical observations of stars analogous to the sun are used to construct a tentative account of the evolution of solar UV luminosity. Evidence exists that the young sun was a much more powerful source of energetic particles and radiation than it is today, and while on the main sequence, solar activity has declined as an inverse power law of age as a consequence of angular momentum loss to the solar wind. Observations of pre-main sequence stars indicate that before the sun reached the main sequence, it may have emitted as much as ten thousand times the amount of ultraviolet radiation that it does today. The impact of the results on knowledge of photochemistry and escape of constituents of primordial planetary atmospheres is discussed.

Zahnle, K. J.↗
NASA NTRS1982

The effects of ejecta on the X-ray luminosities of supernova remnants

Because X-ray luminosities of most SNRs are dominated by emission from heavy elements, estimates of the X-ray emitting mass based on cosmic abundances may be incorrect. Here we investigate the apparent density evolution of a SNR when substantial amounts of processed material are ejected by the supernova. If this material is shock heated, it will dominate X-ray emission from the remnant long after the SNR has swept up the equivalent amount of interstellar matter (ISM). Emission from metal-rich ejecta may explain why ISM densities of young remnants far from the galactic plane, deduced from standard analysis, are higher than expected, as well as why larger SNRs appear to be lying in regions of lower ISM density. It should be included in detailed calculations of SNR surface brightness distributions, along with effects due to departures from ionization equilibrium and cloudlet evaporation in a multiphase ISM which may also contribute to the apparent evolution of density with radius.

Long, K. S.↗
NASA NTRS1983

Far-infrared detection of low-luminosity star formation in the Bok globule B335

Measurements of far-infrared intensities in the Bok globule B335, made with higher spatial and spectral resolution than two earlier studies, are described. The NASA 3-m Infrared Telescope Facility was used in February 1981 and the Kuiper Airborne Observatory 0.9-m telescope was used in October 1981 and August 1982 for the observations. The far-infrared source in B335 was revealed to be more compact than previously assumed, ruling out the interstellar radiation field as the dominant heat source. The new far-infrared size, luminosity, and temperature derived suggest that these may be the first observations of low-mass star formation embedded deeply within a Bok globule. The far-infrared source does not have a near-infrared or radio continuum counterpart. High angular resolution at submillimeter wavelengths will be critical in further studies of low-mass star formation.

Davidson, J. A.↗
NASA NTRS1984

Limits on the infrared and visual luminosity of the intergalactic H I cloud in Leo

Low surface brightness photometry of the intergalactic neutral hydrogen cloud in Leo sets upper limits on the intensity of this object of 28.0 mag/sq arcsec in the V photometric band and 22.8 mag/sq arcsec in the K band. The corresponding ratio of the H I mass to blue luminosity in the H I emission peaks of the cloud must be greater than 2.9 (solar units) depending on the star formation history of the object. The limits imposed on the star formation rate suggest a strong dependence of this rate on gas density.

Skrutskie, M. F.↗
NASA NTRS1984

The 157 Micron (C II) Luminosity of the Galaxy

The diffuse far infrared (C II) emission of several regions of the Galactic plane were sampled. Mechanisms for the excitation of carbon ions are discussed in reference to the role of carbon ion transitions in cooling diffuse atomic hydrogen. Observations indicate that the C II emission probably arises at the edges of giant molecular clouds and appears to have localized knot-like features. The total C II luminosity of the Galaxy is approximately 6 to 10 to the 7th power L(solar).

Stacey, G. J.↗
NASA NTRS1984

STS atmospheric luminosities

During the STS-8 space shuttle mission special photographic and TV operations were carried out to record the properties of the spacecraft induced luminosities. One of these luminous phenomena is the quiescent vehicle glow which was photographed during the STS-8 mission with an image intensified photographic camera, with and without an objective grating. During the latter part of the mission the altitude of the shuttle was relatively low (120 n.m. = 222 km) and unprecedentedly high intensity of the glow was observed. The crew reported that the glow was easily visible to the naked eye. The proper orientation of the shuttle with respect to the velocity vector and the objective grating permitted the exposure of good objective spectrum of the glow in the visible region. From the results it is clear that the spectrum appears to be a continuum as observed by the image intensifier objective grating camera. Qualitative examination of the data shows that there is very tail little glow ion the wavelength range of 4300 to about 5000 angstroms. Above 5000 angstroms the glow becomes stronger towards the red and then it falls off towards higher wavelength and of the spectrum presumably because of the responsivity of the device.

Mende, S. B.↗
NASA NTRS1984

Luminosity and spatial distribution of the forbidden O I 6300-A emission in comets

The Tuttle, Stephan-Oterna, and Brooks 2 comets have been subjected to CCD observations of the 6300 and 6364 A forbidden oxygen lines, in order to determine the spatial profiles and absolute luminosities of the cometary forbidden O I lines. Analysis indicates the source of the observed O I photons to be direct photodissociation of water vapor. O 1D production by dissociation of OH becomes dominant at larger distances from the nucleus, and the water vapor production rates derived from O I emissions are found to be in good agreement with those determined from forbidden line OH by the IUE spacecraft, as well as ground-based photometry. It is demonstrated that analysis of cometary O 1D emission allows the determination of the spatial distribution of the parent molecule water vapor.

Fink, U.↗
NASA NTRS1985

Mass loss rates from protostars and OI(63 micron) shock luminosities

The high-velocity ejection of material from protostars results in a wind shock which may be observable in OI(63 micron) emission. It is shown that for a wide range of conditions, the OI(63 micron) luminosity is proportional to the mass loss rate from the protostar. Application is made to shock OI(63 micron) emission observed around IRc2 in the BN-KL region of Orion.

Hollenbach, D.↗
NASA NTRS1985

The 157-micron forbidden C II luminosity of the Galaxy. II - The presence of knotlike features in the forbidden C II emission

The measurement by Stacey et al. (1983) of the diffuse 157-micron emission of singly ionized carbon from the Galactic plane is augmented by measurements at two additional galactic longitudes. The results indicate that the total forbidden C II flux from the Galaxy is about 6 x 10 to the 7th solar luminosity - a factor of 8 lower than the previous estimate. It is likely that the measurement at l(II) = 8.0 deg was due to a knot in the forbidden C II emission. The results indicate that the forbidden C II flux has a half width of roughly 0.34 deg, in agreement with the (C-12)O (J = 1-0) half widths. The forbidden C II emission probably arises in at the edges of molecular clouds.

Stacey, G. J.↗
NASA NTRS1985

A redetermination of the luminosity, distance, and reddening of Beta Lyrae

The most likely distance to the Beta Lyrae system is redetermined to lie at 370 pc, corresponding to a distance modulus of 7.8 mag, while the correct modulus value probably lies in the 7.7-8.0 mag range, corresponding to a distance range between 345 and 400 pc. On the basis of Wilson's (1974) model, the phase-averaged absolute visual magnitude of the primary component is -4.1 mag; this star is therefore a very luminous giant, classifiable as B8.5 or B9, with a luminosity class of II-Ib. The present data are based on optical and IUE scans of the brightest visual companion to Beta Lyrae, HD 174664, together with an analysis of the H line profiles in its spectrum.

Dobias, J. J.↗
NASA NTRS1986

Fe II emission line profiles in spectra of high luminosity non-coronal stars

The results of a program to study the winds of noncoronal late-type giant and supergiant stars with IUE are presented. The primary data for this study are profiles, fluxes, and velocities of the Fe II emission lines which occur throughout the 2200 to 3230 A region of the IUE long wavelength spectrographs. The apparent dependence of the Fe II profiles on stellar luminosity (surface gravity) and intrinsic line strength is discussed. The discovery of significant changes in the Fe II profiles in spectra of Gamma Crucis (M3 III), during the period 1978 to 1985, that suggest a substantial change in its outer atmosphere is noted.

Carpenter, Kenneth G.↗