X-ray data analysis of VW Hyi with XMM-Newton observatory

Cataclysmic variables (CV) are compact binary star systems in which matter is transferred from a Roche Lobe filling main-sequence star onto a white dwarf. It is already known that outbursts correlate with the amount of mass transfer from secondary onto white dwarf. While shell ejection does not occur during dwarf nova outbursts, novae have ejected shells. In this thesis, a spectral analysis of the dwarf nova VW Hyi (which is a CV) is presented. The system was observed during the quiescent state with the XMM-Newton satellite sensitive to Ex ? 15 keV. X-ray bolometric flux of boundary layer (EX < 2 keV) is estimated to be ~ 6,7 x 10-12 erg cm-2 s-1 and entire boundary layer luminosity, LX = 6,8 x 1030 erg / s. Measurements by PN+MOS detector on XMM indicate that X-ray emitting maximum plasma temperature is kTmax = 6,28 keV according to "Cevmkl Xspec" spectral model. The ratio of boundary layer to disk luminosity is found to be Lsınır / Ldisk ~ 0,2. The X-ray spectra analysis indicate the presence of a hot and thin plasma (optically) in the boundary layer that cools via an isobaric cooling flow while settling onto the white dwarf. Fe XXV and Fe XXVI lines are originated from a plasma having temperature of 10^7 - 10^8 K. The Fe XXVI line at 6,9keV, clearly demonstrates that plasma at higher temperatures is either not present or not radiating efficiently in X-rays. For kTmax = 6,28 keV, the rate of accretion from the boundary layer on to the white dwarf is estimated to be =2,71 x 1014 gr / sn = 4,3 x 10-12 M ? /yr.VW Hyi is a system which shows ultraviolet delay because the outburst in ultraviolet wavelenghts occurs approximately one day later than that in optical wavelenghts. One of the models which can explain this delay is Coronal Siphon Model. At the end of the spectral analysis in this study, thin boundary layer evaporates according to coronal siphon model and then it settle down to white dwarf becoming cold from the corona.