The Hot White Dwarf in the Cataclysmic Variable MV Lyrae

Abstract

We have obtained the first far-ultraviolet spectrum of the nova-like cataclysmic variable MV Lyrae using the Far Ultraviolet Spectroscopic Explorer (FUSE). We also obtained contemporaneous optical light curves and spectra. All data are from a deep faint accretion state of MV Lyr. We constructed a model for the system using the BINSYN software package; results from this model include the following: (1) The white dwarf has T_eff=47,000K, photospheric logg=8.25, and metallicity of Z~0.3Z_solar. (2) The secondary star is cooler than 3500 K; it contributes nothing to the far-ultraviolet flux and a varying amount to the optical flux (from 10% at 5200 Å to 60% at 7800 Å). (3) The accretion disk, if present at all, contributes negligibly to the spectrum of MV Lyr. Irradiation considerations imply that the mass transfer rate is no more than 3×10^-13M_solaryr^-1. (4) Assuming no disk is present, the model optical light curve has an amplitude approximately 50% larger than that of the sinusoidal modulation (on the orbital period) in the observed optical light curve, suggesting that the secondary star might be shaded by a nascent disk and/or have starspots near the L1 point. (5) The scaling of the model spectrum to the observed data leads to a distance of d=505+/-50pc to MV Lyr.

This research is based on observations with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985, and on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium.