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Ultraviolet spectroscopic observations of HD 77581 (Vela X-1 = 4U 0900-40)
Sadakane, K.; Hirata, R.; Jugaku, J.; Kondo, Y.; Matsuoka, M.; Tanaka, Y.; Hammerschlag-Hensberge, G.
AA(Osaka University of Education, Osaka, Japan), AB(Kyoto, University, Kyoto, Japan), AC(Tokyo Astronomical Observatory, Mitaka, Japan), AD(Tokyo, University, Tokyo, Japan), AE(Tokyo, University, Tokyo, Japan), AF(Tokyo, University, Tokyo, Japan), AG(Amsterdam, Universiteit, Amsterdam, Netherlands)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 288, Jan. 1, 1985, p. 284-291. Research supported by the Japan Society for the Promotion of Science. (ApJ Homepage)
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NASA/STI Keywords:
Binary Stars, Stellar Spectra, Ultraviolet Spectra, X Ray Sources, Aluminum, Iron, Iue, Photosphere, Radial Velocity, Spectrum Analysis, Stellar Temperature, Stellar Winds
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Ultraviolet spectra of HD 77581 obtained with the IUE satellite in December 1982 and January 1983 are analyzed. The effective temperature is found to be 25,000 + or - 1000 K by comparing its photospheric absorption lines with those in four well-studied B0-B1 supergiants. The distance of 1.9 + or - 0.2 kpc is derived from its luminosity log L/solar-L = +5.53, which is obtained from the effective temperature and from its radius. Circumstellar matter is detected not only in the C IV and Si IV lines but also in Al III, Fe III, C II, and Mg II lines. Profiles of the C IV and Si IV lines show a similar dependence on the orbital phase as in 1978. Two distinct sharp components are found in the shortward-shifted absorptions of the Al III and Fe III lines. Once component is present only in the second half of the orbital period, and its origin may be a 'trailing wake' behind the neutron star. The other component is seen all over the period, and it can be interpreted as originating in a cool expanding region of gas in the orbital plane.

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