A multiwavelength timing analysis of the eclipsing polar DP Leo

Free access article

Issue		A&A Volume 392, Number 2, September III 2002


Page(s)		541 - 551
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20011651

A&A 392, 541-551 (2002)
DOI: 10.1051/0004-6361:20011651

A multiwavelength timing analysis of the eclipsing polar DP Leo

A. D. Schwope¹, V. Hambaryan¹, R. Schwarz¹, G. Kanbach² and B. T. Gänsicke³

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
³ Deptartment of Physics and Astronomy, University of Southampton, Hampshire, Southampton, SO17 1BJ, UK

(Received 3 August 2001 / Accepted 17 June 2002 )

Abstract
We present an analysis of the X-ray light curves of the magnetic cataclysmic variable DP Leo using recently performed XMM-Newton EPIC and archival published and unpublished ROSAT PSPC observations. We combine the timings of the X-ray eclipses with timings derived from archival HST-observations and new optical observations with the photon counting OPTIMA camera. We determine the eclipse length at X-ray wavelengths to be $235\pm5$ s, slightly longer than at ultra-violet wavelengths, where it lasts 225 s. A new orbital ephemeris is derived which connects the more than 120 000 binary cycles covered since 1979. It has a highly significant quadratic term, implying an orbital period change of $\dot{P} = -4.4 \times 10^{-12}$ s s ^-1, two orders of magnitude larger than being compatible with braking by gravitational radiation only. Over the last twenty years, the optical and X-ray bright phases display a continuous shift with respect to the eclipse center by ~ $2.1\degr$ yr ^-1. Over the last 8.5 years the shift of the X-ray bright phase is ~ $2.5\degr$ yr ^-1. We interpret this as evidence of an asynchronously rotating white dwarf although synchronization oscillations cannot be ruled out completely. If the observed phase shift continues, a fundamental rearrangement of the accretion geometry must occur on a time-scale of some ten years. Applying model atmosphere spectra to optical/UV eclipse light curves, we determine the temperature and mass of the white dwarf, the temperature and size of the optical/UV emitting spot and the distance to DP Leo to be $T_{\rm wd} = 13\,500$ K, $M_{\rm wd} \simeq 0.6$ $M_\odot$ , $T_{\rm spot} = 32\,000$ K, $A_{\rm spot} \simeq 0.1~A_{\rm wd}$ , and D = 400 pc, respectively. The implied inclination and mass ratio are $i=79.5\degr$ and $Q = M_{\rm wd}/M_2 = 6.7$ . DP Leo is marginally detected at eclipse phase in X-rays. The upper limit eclipse flux is consistent with an origin on the late-type secondary, $L_{\rm X} \simeq 2.5 \times 10^{29}~{\rm ergs~s}^{-1}$ (0.20-7.55 keV), at a distance of 400 pc.

Key words: stars: binaries: eclipsing -- stars: novae, cataclysmic variables -- stars:individual: DP Leo -- X-rays: stars

Offprint request: A. D. Schwope, aschwope@aip.de

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.