XMM-Newton observations of OY Car III: OM light curve modelling, X-ray timing and spectral studies

¹ Observatory, PO Box 14, 00014 University of Helsinki, Finland
² Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey, RH5 6NT, UK

Corresponding author: P. Hakala, pasi.hakala@astro.helsinki.fi

Received: 8 July 2003
Accepted: 3 December 2003

Abstract

We revisit the XMM-Newton observations of the dwarf nova OY Car taken in July 2000 which occured shortly after an outburst. Ramsay et al. ([CITE]) found a prominent energy dependent modulation at a period of 2240 s: this modulation was only seen for ~1/3 of the observation duration. In our new analysis, we examine this time interval in greater detail. In addition to the 2240 s period we find evidence for other periods, the most prominent being near 3500 s. Both these modulations are most likely due to changes in photoelectric absorption over this period: this is supported by phase-resolved spectroscopy. This may indicate the presence of matter above the accretion disc or a presence of a magnetic accretion curtain. In this case the 2240 s period could represent a spin period of the white dwarf and the 3500 s period a beat period between the spin and orbital periods. We also model the B band and UV eclipse profiles and light curves using a new technique to map the spatial extent of the accretion disc. As a result we find that whilst the optical emission is dominated by both the emission close to the accretion disc boundary layer and the hot spot where the accretion stream hits the disc, the UV emission is mainly dominated by the inner disc/boundary layer only.