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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Energy distributions and radiation transport in uranium plasmas

An approximate analytic model, based on continuous electron slowing, has been used for survey calculations. Where more accuracy is required, a Monte Carlo technique is used which combines an analytic representation of Coulombic collisions with a random walk treatment of inelastic collisions. The calculated electron distributions have been incorporated into another code that evaluates both the excited atomic state densities within the plasma and the radiative flux emitted from the plasma.

Miley, G. H.↗
NASA NTRS1978

Near-infrared energy distributions of M31

Spectrophotometric data obtained by comparing Spinrad-Taylor (1969) standards with Alpha Lyr are presented, along with a calibration of these data for wavelengths longward of 6000 A. M31 sky measurements made 1 deg south of the nucleus at five wavelengths between 6040 and 10,360 A, inclusive, are compared with near-IR spectrophotometry performed by Spinrad and Taylor (1971), Oke and Schwarzschild (1975), and O'Connell (1976). Agreement and discrepancies among the different data sets are discussed. Some possible explanations of the differences are discounted, and tests are performed which reveal no effects of error in mean extinction and brightness-dependent wavelength response.

Taylor, B. J.↗
NASA NTRS1981

Stepanian's star - The energy distribution reveals a nontypical cataclysmic variable

Einstein, IUE, optical multichannel spectrophotometry, and IR observations of Stepanian's star are discussed in terms of other known cataclysmics. While the X-ray flux and IUE emission-line data are similar to that of dwarf novae, the total continuum flux distribution from uv-IR is cooler (peaking near a 10,000 K blackbody) and is unlike either a stellar component or a classic steady-state disk. The IR data show no evidence for a late-type component.

Szkody, P.↗
NASA NTRS1982

Infrared/optical energy distributions of high redshifted quasars

Measurements at 1.2, 1.6 and 2.2 microns were combined with visual spectrophotometry of 21 quasars having redshifts z or = 2.66. The primary result is that the rest frame visual/ultraviolet continua of the high redshift quasars are well described by a sum of a power law continuum with slope of approximately -0.4 and a 3000 A bump. The rest frame visual/ultraviolet continua of these quasars are quite similar to that of 3C273, the archetype of low redshift quasars. There does not appear to be any visual/ultraviolet properties distinguishing high redshift quasars selected via visual or radio techniques.

Soifer, B. T.↗
NASA NTRS1982

Spectral energy distribution /119 - 685 nm/ in 16 shell stars and a tentative model for accreting Be stars

IUE low-dispersion spectra and spectral scans made with the Lick Observatory IDS scanners have been combined for 16 shell stars. Eleven objects can be represented by Kurucz (1979) model atmospheres, although some of them display strong shell-type line spectra. Five among them are known binaries. The six remaining objects display complex spectra. A model involving continuum and line radiation from a hydrogen cloud surrounding the accreting component is proposed. A generalization of this model with optically thick segments of the cloud promises to explain even more exotic objects such as beta Lyrae, W Serpentis and possibly epsilon Aurigae.

Plavec, M. J.↗
NASA NTRS1984

The far-ultraviolet energy distribution of Sirius B from Voyager 2

Observations of Sirius obtained with the Voyager 2 ultraviolet spectrometer clearly reveal the presence of flux from the white dwarf Sirius B at wavelengths between 950 and 1100 A. These observations are in good agreement with all previous ultraviolet observations of Sirius B, and in particular with the IUE observations of Boehm-Vitense, Dettmann, and Kapranidis. A joint analysis of the Voyager 2 and IUE observations yields a temperature range of 26,000-28,000 K. A reexamination of current ultraviolet, visible, and X-ray observations produces good general agreement, but no single, mutually consistent, temperature for Sirius B. The Voyager 2 observations can be used to place a firm upper limit of 28,000 K on the temperature of Sirius B.

Holberg, J. B.↗
NASA NTRS1985

On the ultraviolet energy distributions and the temperatures of peculiar B and A stars

Color temperatures have been estimated by comparing ultraviolet observations of HgMn and magnetic Ap stars with those of normal stars. Ultraviolet data from the OAO-2, ANS, TD-1, and IUE satellites generally give similar results. The values for the normal stars were derived from comparison of fluxes predicted by solar-composition fully line-blanketed model atmospheres with optical region spectrophotometry. The ultraviolet temperatures of the HgMn stars cover a narrower temperature range than do their optical region values. Magnetic Ap stars with similar optical region temperatures can show substantial differences in their ultraviolet color temperatures. This may result from magnetic field configuration and abundance differences.

Adelman, S. J.↗
NASA NTRS1987

Ultraviolet interstellar extinction toward NGC 6530 and the intrinsic energy distribution of 9 Sagittarii and HD 165052

The ultraviolet interstellar extinction curve is determined toward 12 early B main-sequence stars and one O8 V star in NGC 6530. The extinction is found to be uniform across the cluster. At short wavelengths, the extinction curve of NGC 6530 falls below the average Galactic curve by a full magnitude, indicating that the population of small grains relative to larger grains is lower than normal. Longward of 2830 A the curve is almost coincident with the mean Galactic curve. The 2175 A feature is narrower than the average. The derived extinction curve is used to deredden the observed fluxes of two early O-type stars in NGC 6530:9 Sgr and HD 165052. The intrinsic continua are compared to model atmospheres in the region 1200-8200 A. The LTE, line-blanketed models of Kurucz (1979) fit the observations better than the non-LTE, unblanketed models of Mihalas (1972) suggesting that line-blanketing effects are more important than the non-LTE effects in the atmospheres of these stars. The temperatures of the models that best fit the observations are lower than the Zanstra temperatures and the temperatures estimated from the strengths of the He I and He II lines, by 10,000 to 20,000 K.

Torres, Ana V.↗
NASA NTRS1988

Energy distribution and variability of BL Lac objects - Recent observations and a theoretical scheme

Spectral properties of X-ray selected and radio-selected BL Lacs are discussed. The results provide a direct indication that the X-ray emission is more isotropic than the radio emission. Recent results of multifrequency observations of the brightest X-ray selected BL Lac object, PKS 2155-304, are reviewed, showing how the fast X-ray variability is smeared out at low frequencies. A theoretical jet model is presented which can quantitatively account for the different spectral properties of X-ray selected and radio selected BL Lacs in terms of different line-of-sight angles to the jet.

Maraschi, L.↗
NASA NTRS1989

Intrinsic ultraviolet (912-3200 A) energy distribution of OB stars

Low-dispersion 500-3200-A spectra of 20 OB stars are used to derive three individual extinction curves in the wavelength range 912-1200 A. The dependence of the intrinsic UV fluxes of OB stars on both spectral type and luminosity is demonstrated. UV color indices are proposed. The results confirm the previous finding that O star spectra are not significantly bluer than the spectrum of the B0 main-sequence star Upsilon Ori.

Longo, Renata↗