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Astron. Astrophys. 339, L21-L24 (1998)

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Letter to the Editor

On the X-ray properties of V Sge and its relation to the supersoft X-ray binaries

Jochen Greiner 1 and André van Teeseling 2

1 Astrophysical Institute Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany
2 Universitäts-Sternwarte Göttingen, Geismarlandstrasse 11, D-37083 Göttingen, Germany

Received 14 August 1998 / Accepted 15 September 1998


We investigate the ROSAT X-ray properties of V Sge, which has been proposed to be related to supersoft X-ray binaries. During optical bright states, V Sge is a faint hard X-ray source, while during optical faint states ([FORMULA] mag), V Sge is a `supersoft' X-ray source. Spectral fitting confirms that V Sge's X-ray properties during its soft X-ray state may be similar to those of supersoft X-ray binaries, although a much lower luminosity cannot be excluded. It is possible to explain the different optical/X-ray states by a variable amount of extended uneclipsed matter, which during the optical bright states contributes significantly to the optical flux and completely absorbes the soft X-ray component. An additional, perhaps permanent, hard X-ray component, such as a bremsstrahlung component with a 0.1-2.4 keV luminosity of [FORMULA] erg s-1, must be present to explain the X-ray properties during the optical bright/hard X-ray state.

Key words: accretion disks – cataclysmic variables – eclipsing binaries – X-rays: stars – stars: individual: V Sge

Send offprint requests to: J. Greiner (e-mail: jgreiner@aip.de)

© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998