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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 NTRS1982

The effect of perturbation of convective energy transport on the luminosity and radius of the sun

The response of solar models to perturbations of the efficiency of convective energy transport is studied. Such perturbations primarily affect the shallow superadiabatic layer of the convective envelope. Independent of the details of the perturbation scheme, the resulting change in the solar radius is always very small compared to the change in luminosity. This appears to be true for any physical mechanism of solar variability which operates in the outer layers of the convection zone. Changes of the solar radius have been inferred from historical observations of solar eclipses in 1715 and 1925. Considering the constraints on concurrent luminosity changes, this type of solar variability must be indicative of changes in the solar structure at substantial depths below the superadiabatic layer of the convective envelope.

Endal, A. S.↗
NASA NTRS1983

Upper Limits to the Annihilation Radiation Luminosity of Centaurus a

A high resolution observation of the active nucleus galaxy Centaurus A (NGC 5128) was made by the GSFC low energy gamma-ray spectrometer (LEGS) during a balloon flight on 1981 November 19. The measured spectrum between 70 and 500 keV is well represented by a power law of the form 1.05 x 10 (-4) (E/100 keV) (-1.59) ph/sq cm /s with no breaks or line features observed. The 98% confidence (2 sigma) flux upper limit for a narrow ( 3 keV) 511-keV positron annihilation line is 9.9 x 10 (-4) ph/ sq cm /s. Using this upper limit, the ratio of the narrow-line annihilation radiation luminosity to the integral or = 511 keV luminosity is estimated to be 0.09 (2 sigma upper limit). This is compared with the measured value for our galactic center in the Fall of 1979 of 0.10 to 0.13, indicating a difference in he emission regions in the nuclei of the two galaxies.

Gehrels, N.↗
NASA NTRS1982

Evolution of the cluster X-ray luminosity function slope

The results of an X-ray survey of 58 clusters of galaxies at moderate and high redshifts are reported. Using a luminosity-limited subsample of 25 objects, it is found that to a redshift of 0.5 the slope of the luminosity function of distant clusters is independent of redshift and consistent with that of nearby clusters. The time scale for change in the slope must be greater than 9 billion years. The implications of the data for theoretical models are discussed. In particular, Perrenod's models (1980) with high Omega are excluded by the present data.

Henry, J. P.↗
NASA NTRS1982

Derivation of the luminosity of a gamma ray burst

The intrinsic luminosity, erg/s, in a gamma ray burst is calculated using two assumptions: first, the power is independent of the burst duration, and, second, the spatial distribution of the bursters is similar to the spatial distribution of the pulsars. It is found that the experimentally determined distribution of burst durations is significantly biased by the observational selection effects. It is shown that a typical luminosity of 5 x 10 to the 35th erg/s can adequately reproduce the burst (log N, log S) curve, an isotropic latitude distribution, and the experimentally determined distribution of durations.

Higdon, J. C.↗
NASA NTRS1983

Soft X-ray spectral observations of quasars and high X-ray luminosity Seyfert galaxies

Results of the analysis of 28 Einstein SSS observations of 15 high X-ray luminosity (L(x) 10 to the 435 power erg/s) quasars and Seyfert type 1 nuclei are presented. The 0.75-4.5 keV spectra are in general well fit by a simple model consisting of a power law plus absorption by cold gas. The averager spectral index alpha is 0.66 + or - .36, consistent with alpha for the spectrum of these objects above 2 keV. In all but one case, no evidence was found for intrinsic absorption, with an upper limit of 2 x 10 to the 21st power/sq cm. Neither was evidence found for partial covering of the active nucleus by dense, cold matter (N(H) 10 to the 22nd power/sq cm; the average upper limit on the partial covering fraction is 0.5. There is no obvious correlation between spectral index and 0175-4.5 keV X-ray luminosity (which ranges from 3 x 10 to the 43rd to 47th powers erg/s or with other source properties. The lack of intrinsic X-ray absorption allows us to place constraints on the density and temperature of the broad-line emission region, and narrow line emission region, and the intergalactic medium.

Petre, R.↗
NASA NTRS1984

Far-infrared and submillimeter observations of the low-luminosity protostars L1455 FIR and L1551 IRS 5 - The confinement of bipolar outflows

Far-IR observations of L1455 FIR and L1551 IRS 5 obtained in December, 1981, and in September, 1982, and January, 1983, respectively, using the H-1 and G-2 bolometer systems on the 91-cm telescope of the NASA Kuiper Aiborne Observatory are reported. Additional observations at 400 microns were obtained with UKIRT in November, 1981, (L1551) and with NASA IRTF in November, 1982 (L1455). The results are presented in tables and graphs, and L1455 and L1551 are compared with other objects in terms of central-star parameters, clouds, and overflows. The characteristics calculated for L1455 and L1551 include luminosity 1.5 and 23 solar luminosity, size less than 7 x 10 to the 16th cm, H2 density greater than or equal to 4 x 10 to the 5th and 1 x 10 to the 6th/cu cm, and 35-K dust cores of 0.2 and 0.7 solar mass, respectively. The bipolar appearance of the L1551 outflow is attributed to circumstellar material only.

Davidson, J. A.↗
NASA NTRS1984

Soft X-ray spectral observations of quasars and high X-ray luminosity Seyfert galaxies

Results of the analysis of 28 Einstein SSS observations of 15 high X-ray luminosity (L(x) 10 to the 435 power erg/s) quasars and Seyfert type 1 nuclei are presented. The 0.75-4.5 keV spectra are in general well fit by a simple model consisting of a power law plus absorption by cold gas. The average spectral index alpha is 0.66 + or -0.36, consistent with alpha for the spectrum of these objects above 2 keV. In all but one case, no evidence was found for intrinsic absorption, with an upper limit of 2 x 10 to the 21st power/sq cm. Neither was evidence found for partial covering of the active nucleus by dense, cold matter (N sub H greater than 10 to the 22nd power/sq cm); the average upper limit on the partial covering fraction is 0.5. There is no obvious correlation between spectral index and 0.75-4.5 keV X-ray luminosity (which ranges from 3 x 10 to the 43rd to 47th powers erg/s) or with other source properties. The lack of intrinsic X-ray absorption allows us to place constraints on the density and temperature of the broad-line emission region, and narrow line emission region, and the intergalactic medium. Previously announced in STAR as N84-14082

Petre, R.↗
NASA NTRS1984

Ultraviolet spectral morphology of the O stars - The remarkable luminosity dependence of the Si IV stellar wind effect

An extensive survey of ultraviolet O type spectra, by means of high-resolution data from the International Ultraviolet Explorer archives, shows a strong correlation between both the photospheric and stellar wind features, and the optical spectral types. In particular, the stellar wind effect in the Si IV resonance doublet displays a strong luminosity dependence which has not been completely described before: there is no effect anywhere on the main sequence, but it develops gradually through the intermediate luminosity classes into a full P Cygni profile in the supergiants. This behavior is in sharp contrast to that of the C IV and N V, which have strong P Cygni profiles throughout most of the O type domain, including the main sequence. The Si IV effect simultaneously provides a sensitive classification criterion and poses an outstanding problem for detailed astrophysical interpretation. In addition, a new emission feature at 1574 A, possibly due to N III or to N IV forbidden line, is reported.

Walborn, N. R.↗
NASA NTRS1985

The Feinheit method: A phase-independent formulation of the period-luminosity relation for Cephids

The tight correlation between color and luminosity during the cyclical variation of a Cepheid is calibrated and shown to be a direct means by which most of the phase-dependent temperature-induced amplitude of the variable can be transformed away. The resulting Feinheit function, F = V - alpha (B-V) gives rise to a random-phase period-luminosity relation with an rms scatter of less than 0.20 mag. A comparison shows that the blue Feinheit method for distance determinations method from single-phase observations is as accurate as near-infrared photometry but has the added advantage of being able to use panoramic detectors for the data acquisition. The Feinheit function is identified as the surface area variation of the Cepheid during its cycle.

Madore, B. F.↗
NASA NTRS1983

Upper limits to the annihilation radiation luminosity of Centaurus A

A high resolution observation of the active nucleus galaxy Centaurus A (NGC 5128) was made by the GSFC low energy gamma-ray spectrometer (LEGS) during a balloon flight on 1981 November 19. The measured spectrum between 70 and 500 keV is well represented by a power law of the form 1.05 x 10 (-4) (E/100 keV) (-1.59) ph/sq cm/s with no breaks or line features observed. The 98 percent confidence (2 sigma) flux upper limit for a narrow (3 keV) 511-keV positron annihilation line is 9.9 x 10 (-4) ph/sq cm/s. Using this upper limit, the ratio of the narrow-line annihilation radiation luminosity to the integral or = 511 keV luminosity is estimated to be 0.09 (2 sigma upper limit). This is compared with the measured value for our Galactic center in the Fall of 1979 of 0.10 to 0.13, indicating a difference in the emission regions in the nuclei of the two galaxies.

Gehrels, N.↗
NASA NTRS1985

A new luminosity component in 3C 48

The infrared emission from the quasar 3C48 has a luminosity L approximately 5 x 10 to the 12th power solar luminosity and dominates the power output of the quasar system. It is shown that the infrared emission, unlike that of most radio loud quasars, is most likely not an extension of the radio emission of the quasar. It is argued that the infrared emission in 3C48 is probably thermal radiation arising in a highly luminous galaxy surrounding the quasar.

Neugebauer, G.↗
NASA NTRS1985

Galaxy luminosity functions, M/L ratios, and closure of the Universe - Numbers and problems

Data on the luminosity function (LF) of galaxies are reviewed and compared, and the result of Kirshner et al. (1983) giving a 'standard LF' is chosen as a best guess. Departures from the 'standard LF' for specific galaxy types and environments (clusters, groups, field) are discussed briefly. A luminosity density of about 1.4 x 10 to the -2nd h 'galaxies' per cubic megaparsec is obtained. The mean M/L ratio needed to give critical cosmological density (Omega sub 0 = 1) is then 920 h in solar units on the face-on magnitude system. Comparison with measured M/L ratios for galaxies and clusters, and with constraints imposed by inflation and nucleosynthesis, poses two problems of 'invisible mass'.

Felten, J. E.↗
NASA NTRS1986

Edddington luminosities and photospheric radius expansion during X-ray bursts from 4U/MXB 1820-30

The analysis of six X-ray bursts from 4U/MXB 1820-30 (one observed in May 1975, and five in March 1976) is presented. In all cases, photospheric contraction during burst decay was observed. The contraction manifests itself as a distinct hardening of the burst spectra, a phenomenon which was previously noted but misinterpreted. The photospheric expansion which must have preceded the contraction takes place in less than one second. The bolometric burst peak luminosities are all near the Eddington limit. This burst source has the best-known distance of all burst sources. These results are therefore of particular interest because of the many reports of super-Eddington burst peak luminosities from sources whose distances are not so well known.

Vacca, W. D.↗
NASA NTRS1987

Stellar bars and the spatial distribution of infrared luminosity

Ground-based 10 micron observations of the central region of over 100 infrared luminous galaxies are presented. A first order estimate of the spatial distribution of infrared emission in galaxies is obtained through a combination of ground-based and Infrared Astronomy Satellite (IRAS) data. The galaxies are nearby and primarily noninteracting, permitting an unbiased investigation of correlations with Hubble type. Approximately 40% of the early-type barred galaxies in this sample are associated with enhanced luminosity in the central (approximately 1 kpc diameter) region. The underlying luminosity source is attributed to both Seyfert and star formation activity. Late-type spirals are different in that the spatial distribution of infrared emission and the infrared luminoisty are not strongly dependent on barred morphology.

Devereux, Nicholas↗
NASA NTRS1987

Optical and IR luminosity functions of IRAS galaxies

The optical and infrared luminosity functions are determined for a 60 micron flux-limited sample of 68 IRAS galaxies covering a total area of 150 deg sq. The IR function is in good agreement with that obtained by other authors. The shape of the optical luminosity function is similar to that of optically selected galaxy samples. The integrated light of most objects in the sample have (NII) to H alpha line flux ratios characteristic of HII-region galaxies. In the absolute magnitude range M sub J = -18, -22 about 14% of late-type galaxies are IRAS galaxies. The apparent companionship frequency is about twice as large as that for a comparable sample of non-IRAS late-type galaxies.

Vader, J. Patricia↗
NASA NTRS1987

The UV excess of quasars - Luminosity dependence

The transition from the near-infrared power law to the blue bump in quasar spectra is studied by analyzing the complete sample published by Neugebauer et al. (1987). It is found that the flattening of the continuum spectrum toward the UV increases with continuum luminosity; the spectral slope between 4200 A and 7500 A (in the quasar's rest frame) is strongly correlated with luminosity and redshift. Only part of this correlation can be attributed to contamination by starlight of the host galaxy. This result is modeled in terms of an accretion disk spectrum combined with a nonthermal power law. In order to fit the data, the Eddington ratio must be in the range L(opt)/L(E) approximately 0.003-0.03(epsilon/0.1) exp -1 (epsilon being the efficiency). This parameter range also yields inner disk temperatures of (30,000-200,000 K), in accordance with the temperatures inferred from the UV excess of quasars observed with the IUE.

Wandel, Amri↗
NASA NTRS1987

Low-Luminosity embedded sources and their environs

A far-infrared and submillimeter study of regions within 0.03 pc of the low-luminosity sources embedded in the clouds B335, L723, B361, L1455, and L1551 is presented along with CO molecular line results on the extended environments of these sources out to 0.3 pc. Three of the embedded objects are definite bipolar outflow sources, one may be associated with an observed outflow, and one has no observable outflow. Data on the outflows are combined with determination of the luminosity of the embedded objects, and of the temperature and matter distribution about the sources, to infer the evolutionary stage of the embedded sources.

Davidson, J. A.↗
NASA NTRS1987

Evidence of an infrared luminosity indicator for galaxies

To elucidate the nature of infrared-luminous galaxies discovered with the IRAS satellite, the optical and infrared luminosities of 1161 Markarian galaxies and 2146 'normal' galaxies from the CfA redshift survey are compared. Survival analysis statistical methods that take upper limits fully into account are used. It is found that L(IR)/L(B) is statistically correlated with L(60) in both samples, though they differ in the distribution at low luminosities. The derived correlation shows that L(IR)/L(B) provides an indicator for L(60). Since galaxies selected in unbiased IRAS surveys will have higher L(IR)/L(B) than optically selected galaxies, they are therefore also selected for high L(60).

Feigelson, Eric D.↗