Line-dominated eclipse spectrum of VELA X-1

Details Line-dominated eclipse spectrum of VELA X-1 Line-dominated eclipse spectrum of VELA X-1

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...436l...1n&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 436, no. 1, p. L1-L4

Astronomy and Astrophysics

Astrophysics

41

Eclipsing Binary Stars, K Lines, Light Curve, Pulsars, Spectrum Analysis, Stellar Winds, X Ray Absorption, X Ray Binaries, Energy Spectra, Massive Stars, X Ray Spectroscopy, X Ray Telescopes

Scientific paper

The eclipsing X-ray binary pulsar Vela X-1 (4U 0900-40) was observed with ASCA twice in 1993 June and July covering the total eclipse transition from ingress to egress by the two observations. The pre-eclipse and posteclipse spectra are composed of a heavily absorbed pulsed component and a flat soft component which is ascribed to scattering by the stellar wind. In contrast, only a nonpulsating scattering component is visible during eclipse, and this spectrum is remarkably line dominated with a flat continuum. In addition to an intense 6.4 keV emission line, which is due to fluorescence of iron in low ionization states, prominent line features are obtained at 0.92, 1.34, and 1.82 keV. These lines are identified as the K-alpha lines of He-like ions of neon, magnesium, and silicon. Significant evidence of He-like K-alpha lines is also obtained for sulfur, argon, and iron. An eclipse spectrum dominated by He-like K-alpha emission lines of heavy elements suggests that radiative recombination followed by cascades is the dominant process in the X-ray-irradiated stellar wind, since such a stellar wind forms highly ionized zones of He-like and H-like ions with a relatively low electron temperature of about 100 eV.

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