S. B. Parsons

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.

Skylab ultraviolet stellar spectra: Cool stars with hot secondaries

A hot companion to the G5 III star HR 3080, a single-line spectroscopic binary, has been discovered from spectra in the vacuum-ultraviolet. The companion must be a subdwarf or pre-white dwarf. A list of previously known systems of the zeta Aur and VV Cep type observed with the ultraviolet spectrograph on Skylab is also given. (AIP)

Variable, optically thick plasma in the interacting binaries R Arae and HD 207739

Attention is given to observational evidence for the presence of variable and optically thick extrastellar gas in two binary stars, R Arae and HD 207739, which appear to be in the evolutionary phase immediately preceding or following the short lived supercritical mass transfer phase. In both binaries, spectral lines and energy distributions are variable outside eclipse. 27 references.

Skylab ultraviolet stellar spectra: A new white dwarf, HD 149499 B

A strong ultraviolet continuum, seen at the position of HD 149499 (KO V), is probably due to its 11.8 mag companion. The companion must then be a hot white dwarf. (AIP)

HD 149499 B - The hottest white dwarf

IUE spectra of the white dwarf component of HD 149499, discovered from the Skylab experiments S-019 UV survey, show prominent lines of He II. The star appears to be helium-rich with He/H not less than 1. The ultraviolet fluxes show the temperature to be within the range 70,000-100,000 K, with the most probable value near 85,000 K.

Comparison of winds in the small Magellanic Cloud and galactic early-type stars

IUE low-resolution spectra of 11 OB stars in the Small Magellanic Cloud reveal considerably lower wind velocities than corresponding galactic stars. The reduced efffectiveness of radiative acceleration due to lower abundances of heavy elements in the SMC is believed to be responsible for this effect. The absorption strengths of the SMC P Cygni profiles are somewhat weaker in Si IV and much weaker in C IV. Crude estimates of relative mass-loss rate suggest that the observed differences may be dominated by the differing relative abundances of Si and C, although a lower degree of wind ionization or lower mass-loss rates for the SMC stars cannot be ruled out.

SKYLAB ultraviolet stellar spectra - Emission lines from the Beta Lyrae system

Observations of Beta Lyr with the Skylab S-019 ultraviolet objective-prism spectrograph show numerous emission lines in the region from 1400 to 2300 A. Some variations in line strength between phases 0.25 and 0.50 are seen, which probably explain the shallowness of the OAO-2 light curve at 1910 A. Many of the emission lines are probably due to intercombination transitions, thus confirming the concept that the emission is produced by collisional excitation in low-density clouds of hot gas.

A hot subluminous star - HDE 283048

The star HDE 283048 located at alpha = 3(h)50(m)3, delta = +25 deg 36 min shows a strong ultraviolet continuum. Ground-based observations indicate a hot-dominated composite spectrum. Several lines of evidence suggest that the hot component is a hot subdwarf.

Skylab ultraviolet stellar spectra: the Wolf-Rayet stars

Ultraviolet spectra showing emission lines in the 1300--2000 A region have been obtained of 12 Wolf-Rayet stars. In the WN stars, lines of He ii are dominant although N iv lambda1718 and N iii lambda1805 are also present. C iv lambda1549 absorption and a strong continuum in HD 151932, HD 93131, HD 92740 and HD 190918 indicate that all four stars have companions. In the WC stars, lines of C iii and C iv dominate. N iv lambda1718 and N iii lambda1805 emissions are probably present in HD 165763 and HD 156385. The ultraviolet spectra of

Variable, optically thick, hot plasma observed in interacting binaries

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