EDP Sciences
Free access
Volume 420, Number 1, June II 2004
Page(s) 273 - 281
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20035843

A&A 420, 273-281 (2004)
DOI: 10.1051/0004-6361:20035843

XMM-Newton observations of the dwarf nova YZ Cnc in quiescence

P. Hakala1, G. Ramsay2, P. Wheatley3, E. T. Harlaftis4 and C. Papadimitriou5

1  Observatory, PO Box 14, 00014 University of Helsinki, Finland
2  Mullard Space Science Lab, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
3  Department of Physics & Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
4  Institute of Space Applications and Remote Sensing, National Observatory of Athens, PO Box 20048, Athens 11810, Greece
5  Institute of Astronomy & Astrophysics, National Observatory of Athens, PO Box 20048, Greece

(Received 10 December 2003 / Accepted 4 March 2004)

We present results from the XMM-Newton observations of the dwarf nova YZ Cnc in a quiescent state. We have performed a detailed time series analysis of the resulting light curves. Unusually, we do not detect any orbital modulation in the UV, with only marginal evidence for X-ray modulation on this period. Although there are peaks in the X-ray periodograms at periods less than 5000 s, we attribute them to red noise effects and assign significance to them using a novel approach. The variability in the UV and optical bands can also be modelled as a result of aperiodic variability (red noise) in the system. There is evidence that the UV and X-ray fluxes are anti-correlated with a time delay of about 100 s, with the UV lagging behind the X-ray emission. This anti-correlation is intriguing, but is only present on two occasions lasting several 1000 s each. The X-ray spectrum shows similar emission features to other dwarf novae and is well fitted using a multi-temperature emission model. We measure a relatively high X-ray luminosity of ${\sim}1.4\times 10^{32}$ ergs/s, although this is consistent with a low binary inclination. Finally, we find evidence for a possible -1200 km s -1 blue shift in the fitted Fe K line energies, possibly indicating the presence of an outflow in this low inclination system.

Key words: accretion, accretion disks -- stars: individual: YZ Cnc -- stars: binaries: close -- X-rays: stars -- methods: data analysis

Offprint request: P. Hakala, pahakala@astro.helsinki.fi

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