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Astron. Astrophys. 349, 588-594 (1999)

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The X-ray spectra of VW Hydri during the outburst cycle

H.W. Hartmann 1, P.J. Wheatley 2, J. Heise 1, J.A. Mattei 3 and F. Verbunt 4

1 SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
3 American Association of Variable Star Observers, 25 Birch Street, Cambridge, MA 02138-1205, USA
4 Astronomical Institute, P.O.Box 80000, 3508 TA Utrecht, The Netherlands

Received 28 April 1999 / Accepted 13 July 1999


We report six BeppoSAX X-ray observations of VW Hyi during and after the outburst of Sep 23 1998. The outburst flux is lower than the quiescent flux in the entire observed energy band (0.1-10 keV), in agreement with earlier observations. The X-ray spectra are fitted with two-temperature plasma and cooling flow spectral models. These fits show a clear spectral evolution in X-rays for the first time in VW Hyi: the hard X-ray turn-up after the outburst is reflected in the emission measure and the temperature. Moreover, during outburst the 1.5-10 keV flux decreases significantly. We argue that this is not consistent with the constant flux during a ROSAT outburst observation made eight years earlier. We conclude from this observation that there are significant differences between outburst X-ray lightcurves of VW Hyi.

Key words: accretion, accretion disks – stars: individual: VW Hyi – stars: novae, cataclysmic variables

Send offprint requests to: w.hartmann@sron.nl

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999