Astronomy and Astrophysics an Xmm-newton Timing Analysis of the Eclipsing Polar Dp Leo

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 ROSAT PSPC observations. We determine the eclipse length at X-ray wavelengths to be 235 ± 5 s, slightly longer than at ultraviolet wavelengths, where it lasts 225 s. The implied inclination and mass ratio for an assumed 0.6 M ⊙ white dwarf are i = 79.7 • and Q = M wd /M 2 = 6.7. We determine a new linear X-ray eclipse and orbital ephemeris which connects the more than 120000 binary cycles covered since 1979. 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 • yr −1. Over the last 8.5 years the shift of the X-ray bright phase is ∼ 2.5 • 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 timescale of some ten years. DP Leo is marginally detected at eclipse phase. The upper limit eclipse flux is consistent with an origin on the late-type secondary, L X ≃ 2.5 × 10 29 ergs s −1 (0.20 − 7.55 keV), at a distance of 400 pc. A&A manuscript no. (will be inserted by hand later) Your thesaurus codes are: missing; you have not inserted them