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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

Major variations in solar luminosity.

The solar neutrino problem is considered, giving attention to the experiments conducted to detect solar neutrinos and the possible reasons for the failure to detect neutrinos emitted from the solar interior. According to one suggestion the core of the sun is in a temporarily expanded condition with a consequent lowering in the emitted neutrino flux from the center of the sun. A possible mechanism that could provide the core expansion is proposed. The effects of mixing reactions in the solar interior are discussed together with variations in solar luminosity which might be responsible for the occurrence of the periods of glaciation.

Cameron, A. G. W.↗
NASA NTRS1974

Formation of the luminosity-sensitive O I multiplet at 7774 A

Line profiles and equivalent widths were calculated for the 7774 A multiplet of O I for model atmospheres in the effective temperature range 6000-6500 K for surface gravities in the range log g = 4.0-1.0. A kinetic equilibrium treatment of line formation can partially account for the observed luminosity sensitivity of these lines and considerably modifies the derived microturbulent broadening parameter. Line profiles obtained from kinetic equilibrium line-formation theory are much deeper than LTE profiles, and new observations of Canopus are presented to verify the essential correctness of this treatment.

Johnson, H. R.↗
NASA NTRS1975

A possible width-luminosity correlation of the Ca II K1 and Mg II k1 features

Existing high resolution stellar profiles of the Ca II and Mg II resonance lines suggest a possible width-luminosity correlation of the K1 minimum features. It is shown that such a correlation can be simply understood if the continuum optical depth of the stellar temperature minimum is relatively independent of surface gravity as suggested by three stars studied in detail.

Ayres, T. R.↗
NASA NTRS1975

Skylab ultraviolet stellar spectra - Variation of intensity and structure of strong lines with temperature and luminosity

Objective-prism spectra at ultraviolet wavelengths extending to 1300 A were photographed during the three Skylab missions in a survey covering 9 percent of the sky. Several spectral features, notably resonance lines of C IV and Si IV, show striking variations with stellar temperature and luminosity. Marked P Cygni profiles in C IV and Si IV, indicative of significant outflow of mass, appear in the spectra of all stars with bolometric magnitude brighter than -8.4.

Henize, K. G.↗
NASA NTRS1975

Ultraviolet observations of cool stars. IV - Intensities of Lyman-alpha and Mg II in epsilon Pegasi and epsilon Eridani, and line width-luminosity correlations

A spectrometer on the Copernicus satellite has been used to confirm the existence of a line width-luminosity relation for the Ly-alpha and Mg II 2800-A chromospheric emission lines in K-type stars by observation of a K2 dwarf (epsilon Eri) and a K2 supergiant (epsilon Peg). Combined with previously reported observations of lines in three K giants (alpha Boo, alpha Tau, and beta Gem), the data are consistent with an identical dependence of line width on absolute visual magnitude for the Ca II K, Ly-alpha, and Mg II 2795-A lines. Surface fluxes of Ly-alpha, Mg II 2800-A, and O V 1218-A (upper limit) for epsilon Eri, and of Mg II 2800-A for epsilon Peg are also compared with values reported previously for the three giant stars.

Mcclintock, W.↗
NASA NTRS1976

On Schmidt's Vm estimator and other estimators of luminosity functions

Schmidt's (1968) estimator, sometimes used to calculate the luminosity function from a complete sample of observed objects, can be generalized naively to the case in which the maximum distance for detection is a function of the direction. Though unbiased, this estimator then does not have minimum variance and, in some cases, is inferior to the classical estimator. The classical estimator, however, is biased when the magnitude boxes are not infinitesimal. A generalization of Schmidt's estimator is proposed which is unbiased and usually superior to both Schmidt's and the classical estimator. Variance formulas and numerical examples are given. The results can be used in combining several catalogs.

Felten, J. E.↗
NASA NTRS1976

A new luminosity limit for spherical accretion onto compact X-ray sources

Preheating of infalling gas by emergent X-rays can suppress accretion on to a compact X-ray source. For spherically symmetric accretion, the effect results in a new luminosity limit, orders of magnitude less than the Eddington limit, above which steady flow is impossible. The model may apply to the globular-cluster X-ray sources.

Ostriker, J. P.↗
NASA NTRS1977

A study of the luminosity function for field galaxies

Nine determinations of the luminosity function (LF) for field galaxies are analyzed and compared. Corrections for differences in Hubble constants, magnitude systems, galactic absorption functions, and definitions of the LF are necessary prior to comparison. Errors in previous comparisons are pointed out. After these corrections, eight of the nine determinations are in fairly good agreement. The discrepancy in the ninth appears to be mainly an incompleteness effect. The LF data suggest that there is little if any distinction between field galaxies and those in small groups.

Felten, J. E.↗
NASA NTRS1978

Observations of low luminosity X-ray sources in Vela-Puppis

Results of a study of the X-ray emission from a small portion of the galactic plane near galactic longitude 260 deg are presented. This region contains at least six low luminosity X-ray sources within approximately 10 deg. of PSRO833-45, which is near the center of the Gum Nebula. The X-ray source associated with the Vela pulsar, 4U0833-45, is observed at twice its 4U catalogue intensity. The lack of X-ray pulsations at the pulsar period, the non thermal power law spectrum, and models of the X-ray come from an extended source approximately 1 deg in radius. The observation of a high temperature spectrum in a field of view containing only Puppis A among known sources has led to the discovery of a new OSO-8 source, OSO752-39. Other spectra from this region are discussed.

Pravdo, S. H.↗
NASA NTRS1978

Observations of low-luminosity X-ray sources in Vela-Puppis

Results are presented for a study of the X-ray emission from a small portion of the galactic plane near galactic longitude 260 deg. This region contains at least six low-luminosity X-ray sources within about 10 deg of PSR 0833-45, which is near the center of the Gum nebula. The X-ray source 4U 0833-45, associated with the Vela pulsar, is observed at twice its 4U catalog intensity. The lack of X-ray pulsations at the pulsar period (greater than 99% nonpulsed), the nonthermal power-law spectrum, and models of the X-ray source distribution in this region suggest that a large fraction of the X-rays come from an extended source about 1 deg of arc in radius. The observation of a high-temperature (effective temperature at least 100 million K) spectrum in a field of view containing only Puppis A among known sources has led to the discovery of new OSO 8 source, OS 0752-39. Other spectra from this region are discussed.

Pravdo, S. H.↗
NASA NTRS1979

Low luminosity galactic X-ray sources

The number of low luminosity sources found in the Galaxy has increased from a few to more than two dozen in the past three years. The sources range from isolated hot white dwarfs (HZ43) to normal stellar coronae (alpha Cen), very active coronal stars (RS CVn), flare stars (UV Ceti), interacting winds and stellar surfaces (Algol), and finally to accretion onto white dwarfs (AM Her, steady; U Gem, impulsive). The following review discusses each of these classes in some detail and portrays the wide variety of physical phenomena leading to X-ray emission.

Garmire, G. P.↗
NASA NTRS1980

Cosmological variation of G and the solar luminosity

Teller's analysis of the effects of a varying gravitational constant G on the past solar luminosity is reexamined. It is shown that if Newtonian gravitation is viewed as a nonrelativistic limit of Einstein's theory, there exists (1) a constraint between G and the total mass M of the sun and (2) a change in the radiative energy density-temperature relation, which were not included in Teller's analysis and which change his result from L is about G to the 7th power (found to be unacceptable) to L is about constant, independently of how G might vary with time.

Canuto, V.↗
NASA NTRS1980

Pulsar gamma-rays: Spectra luminosities and efficiencies

The general characteristics of pulsar gamma ray spectra are presented for a model where the gamma rays are produced by curvature radiation from energetic particles above the polar cap and attenuated by pair production. The shape of the spectrum is found to depend on pulsar period, magnetic field strength, and primary particle energy. By a comparison of 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 about 3 x 10 to the 7th power mc sq. A genaral formula for pulsar gamma ray luminosity is determined and is found to depend on period and field strength.

Harding, A. K.↗
NASA NTRS1981

IUE observations of blue halo high luminosity stars

Two high luminosity population II blue stars of high galactic latitude, BD+33 deg 2642 and HD 137569 were observed at high resolution. The stellar spectra show the effect of mass loss in BD+33 deg 2642 and abnormally weak metallic lines in HD 137569. The interstellar lines in the direction of BD+33 deg 2642, which lies at a height z greater than or equal to 6.2 kpc from the galactic plane, are split into two components. No high ionization stages are found at the low velocity component; nor can they be detected in the higher velocity clouds because of mixing with the corresponding stellar/circumstellar lines.

Hack, M.↗
NASA NTRS1979

Masses, radii, temperatures, luminosities and surface compositions of white dwarfs

The masses, radii, temperature, luminosities and compositions of white dwarf stars are discussed, with particular emphasis on those areas in which considerable work remains to be done. It is pointed out that radii for stars of known parallax are available, together with masses and their variance. Consideration is then given to the difficulties involved in the determination of the temperatures of the hottest stars and helium stars by means of Stromgren or multichannel photometry, and it is noted that the frequency of binaries among the hottest degenerates seems too high to be due to chance. Results of IUE observations of the UV spectra of three DA and one DO star are discussed, with attention given to the similarities between UV-derived and ground-based determinations of temperatures and surface gravities. The metal abundances of hydrogen and helium degenerate stars are finally considered, and spectral classes and abundances of the helium atmosphere degenerates are tabulated.

Greenstein, J. L.↗