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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Ultraviolet spectrophotometry from Gemini 11 of stars in Orion

Ultraviolet spectrophotometry in the wavelength region 2600-3600 A is reported for the bright early-type stars beta, eta, gamma, delta, iota, epsilon, sigma, zeta, and kappa Ori. The results are in good agreement with other observations, and, with the possible exception of the supergiants, are in good agreement with recent line-blanketed model atmospheres. There is evidence that the supergiants possess a small ultraviolet deficiency shortward of 3000 A relative to main-sequence stars of similar spectral type. The most extreme example of this phenomenon is the star kappa Ori.

Morgan, T. H.↗
NASA NTRS1979

Vacuum ultraviolet spectrophotometry and effective temperatures of hot stars

Absolutely calibrated ultraviolet stellar spectra from 3100 A to the hydrogen absorption edge at 912 A were obtained on 1977 February 17 by rocket observations above Woomera, Australia. Spectra taken at 15 A resolution have been compared with the observed fluxes from OAO 2 and with recent model-atmosphere fluxes of Kurucz for five hot stars: Gamma (2) Vel, Zeta Pup, Alpha Eri, Beta Cen, and Alpha Vir. The present data give fluxes which are generally lower than those obtained from OAO 2, with the largest deviations of about 20% between 1400 and 1700 A. Agreement with the models is good, although the model fluxes are substantially larger than the observed values below 1200 A. This discrepancy is greater for the higher-temperature stars. Effective temperatures are also determined and are in good agreement with previous results.

Brune, W. H.↗
NASA NTRS1974

Rocket ultraviolet spectrophotometry of Comet Kohoutek /1973f/

On January 5, 1974, the ultraviolet emissions from Comet Kohoutek (1973f) in the spectral range from 1200 to 3200 A were studied with the aid of a rocket carrying two spectrophotometers. In addition to the Lyman alpha line of atomic hydrogen at 1216 A and the (0,0) and (1,1) bands of OH at 3090 and 3142 A, both atomic oxygen (1304 A) and atomic carbon (1657 and 1561 A) were detected.

Feldman, P. D.↗
NASA NTRS1991

Absolute far-ultraviolet spectrophotometry of hot subluminous stars from Voyager

Observations, obtained with the Voyager ultraviolet spectrometers, are presented of absolute fluxes for two well-known hot subluminous stars: BD + 28 deg 4211, an sdO, and G191 - B2B, a hot DA white dwarf. Complete absolute energy distributions for these two stars, from the Lyman limit at 912 A to 1 micron, are given. For BD + 28 deg 4211, a single power law closely represents the entire observed energy distribution. For G191 - B2B, a pure hydrogen model atmosphere provides an excellent match to the entire absolute energy distribution. Voyager absolute fluxes are discussed in relation to those reported from various sounding rocket experiments, including a recent rocket observation of BD + 28 deg 4211.

Holberg, J. B.↗
NASA NTRS1986

Ultraviolet spectrophotometry of three LINERs

Three galaxies known to be LINERs were observed spectroscopically in the ultraviolet in an attempt to detect the presumed nonthermal continuum source thought to be the source of photoionization in the nuclei. NGC 4501 was found to be too faint for study with the IUE spectrographs, while NGC 5005 had an extended ultraviolet light profile. Comparison with the optical light profile of NGC 5005 indicates that the ultraviolet source is distributed spatially in the same manner as the optical starlight, probably indicating that the ultraviolet excess is due to a component of hot stars in the nucleus. These stars contribute detectable absorption features longward of 2500 A; together with optical data, the IUE spectra suggest a burst of star formation about 1 billion yr ago, with a lower rate continuing to produce a few OB stars. In NGC 4579, a point source contributing most of the ultraviolet excess is found that is much different than the optical light distribution. Furthermore, the ultraviolet to X-ray spectral index in NGC 4579 is 1.4, compatible with the UV to X-ray indices found for samples of Seyfert galaxies. This provides compelling evidence for the detection of the photoionizing continuum in NGC 4579 and draws the research fields of normal galaxies and active galactic nuclei closer together. The emission-line spectrum of NGC 4579 is compared with calculations from a photoionization code, CLOUDY, and several shock models. The photoionization code is found to give superior results, adding to the increasing weight of evidence that the LINER phenomenon is essentially a scaled-down version of the Seyfert phenomenon.

Goodrich, R. W.↗
NASA NTRS1979

Ultraviolet spectrophotometry of degenerate stars

Observations of one helium- and three hydrogen-atmosphere degenerates made with the International Ultraviolet Explorer are discussed. Fluxes in the UV give temperatures in good accordance with those determined from the ground and from the ANS satellite data. Profiles of the strong L-alpha absorption in two DA's fit predictions for the expected temperatures. Gravity determination is vitiated by their steep temperature dependence. If one accepts that theoretical predictions should be correct, corrections to the absolute IUE calibration derived are an upward shift of 3-5%, with irregular residuals attaining + or - 7%.

Greenstein, J. L.↗
NASA NTRS1982

Evaluation of ultraviolet spectrophotometry for simultaneous analysis of alkylbenzenes, alkylnaphthalenes, alkylanthracenes/phenanthrenes and total aromatics in mid-distillate fuels

A rapid ultraviolet spectrophotometric method for the simultaneous determination of aromatics in middistillate fuels was developed and evaluated. In this method, alkylbenzenes, alkylnaphthalenes, alkylanthracenes/phenanthracenes and total aromatics were determined from ultraviolet spectra of the fuels. The accuracy and precision were determined using simulated standard fuels with known compositions. The total aromatics fraction accuracy was 5% for a Jet A type fuel and 0.6% for a broadened properties jet turbine type fuel. Precision, expressed as relative standard deviations, ranged from 2.9% for the alkylanthracenes/phenanthrenes to 15.3% for the alkylbenzenes. The accuracy, however, was less for actual fuel samples when compared to the results obtained by a mass spectrometric method. In addition, the ASTM D-1840 method for naphthalenes by ultraviolet spectroscopy was evaluated.

Kim, W. S.↗
NASA NTRS1982

Voyager absolute far-ultraviolet spectrophotometry of hot stars

Voyager observations in the 912-1200 A spectral region are used to indirectly intercompare absolute stellar spectrophotometry from previous experiments. Measurements of hot stars obtained by the Voyager 1 and 2 ultraviolet spectrometers show considerably higher 912-1200 A continuum fluxes than the recent observations of Brune et al. (1979) and Carruthers et al. (1981). The intercomparisons show all observations in basic agreement near 1200 A. The Carruthers et al. flux measurements are preferred down to 1050 A at which point the Voyager and Brune et al. values are respectively 60% higher and 60% lower. Below 1050 A the diasgreement among the observations becomes very large and the fluxes predicted by model atmospheres have been adopted. The pure hydrogen line-blanketed model atmosphere calculations of Wesemael et al. 1980) in comparison with Voyager observations of HZ 43 are used to adjust the Voyager calibration below 1050 A. This adjusted Voyager calibration, which is in good agreement with current model atmosphere fluxes for both early-type stars and DA white dwarfs, will be used for Voyager astronomical observations.

Holberg, J. B.↗
NASA NTRS1985

Two-phase ultraviolet spectrophotometry of the pulsating white dwarf ZZ Piscium

Spectra of the pulsating white dwarf ZZ Psc (= G29-38) were obtained using the International Ultraviolet Explorer. By using a multiple-exposure technique in conjunction with simultaneous ground-based exposure-metering photometry, it was possible to obtain mean on-pulse and off-pulse spectra in the 1950-1310 A wavelength range. The ratio of the time-averaged on-pulse to off-pulse spectra is best fitted by a temperature variation that is in phase with the optical light variation. This result is consistent with the hypothesis that the observed variation is due to a high-order nonradial pulsation. Conventional ultraviolet spectra of ZZ Psc showed broad absorption features at 1390 and 1600 A. These features are also found in the spectra of the cool DA-type white dwarfs G226-29 and G67-23, and appear to increase in strength with decreasing temperature. A possible explanation for the 1600 A feature is absorption by the satellite band of resonance-broadened hydrogen Ly-alpha. Such absorption would also help explain a discrepancy between the observed pulsation amplitude shortward of 1650 A and the predicted amplitudes based on model atmospheres.

Bond, H. E.↗
NASA NTRS1991

Far ultraviolet spectrophotometry of BD +28 4211

The results are reported of a November 1989 rocket flight which recorded a flux-calibrated spectrum of BD +28 4211 from 912 to 1150 A with 1A resolution. BD +28 4211, an SdO-type star, is commonly used as an ultraviolet calibration source in the IUE wavelength band. The present work extends the useful range of this standard shortward of Lyman-alpha. Since previous experiments show marked disparity, this study can be useful in determining a standard in the 912 to 1216 A band.

Cook, Timothy A.↗
NASA NTRS1972

Ultraviolet spectrophotometry of Arcturus from a rocket.

Results of spectrophotometric observations of Arcturus were obtained at the resolution of about 7 A in the wavelength region from 2700 to 4000 A from an Aerobee rocket. Although the payload was capable of obtaining observations shortward of 2700 A, the stellar flux was too weak for meaningful measurements below that wavelength. The most significant feature in the ultraviolet shortward of the atmospheric cutoff is an emission feature at 2800 A identified as the resonance line of the Mg II doublet.

Kondo, Y.↗
NASA NTRS1971

Absolute ultraviolet spectrophotometry of: alpha CMa, gamma Ori, kappa Ori, and alpha Leo; and a continuing calibration program and some preliminary results

Spectral observations of the stars alpha CMa, gamma Ori, kappa Ori, and alpha Leo have been obtained in the range 1150 to 4000 Angstroms, using rocket borne spectrometers. The payloads have a 13-inch diameter telescope, a rotatable concave diffraction grating, and three pulse counting photomultiplier photometers. The laboratory standards used as photometric references derive their primary calibration directly or indirectly from the National Bureau of Standards. An error range of up to + or - 10 percent is attributed to these laboratory standards; + or - 8 percent to the calibration procedure; and + or - 10 percent is assigned as an accidental error range.

Evans, D. C.↗
NASA NTRS1972

Absolute ultraviolet spectrophotometry of Alpha Canis Majoris, Gamma Orionis, Kappa Orionis and Alpha Leonis

Spectral observations of the stars Alpha Canis Majoris, Gamma Orionis, Kappa Orionis and Alpha Leonis have been obtained in the range 1150-4000 A, using rocket borne spectrometers. The payloads have a 13-inch diameter telescope, a rotatable concave diffraction grating, and three pulse counting photomultiplier photometers. The observations are systematically lower than those of Carruthers (1968) at 1270 A, of Smith (1967) at 1376 A, and of Campbell (1970) at 2150 and 2550 A. The data are also about 15 percent lower than the ground-based photometry reported by Schild, Peterson and Oke (1971). The OAO-2 short wavelength scanner calibration agrees with the alpha Leo observations, but disagrees for Kappa Ori and Gamma Ori.

Evans, D. C.↗