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 Teff = 47,000 K, photospheric log g = 8.25, and metallicity of Z ≈ 0.3 Z⊙. (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 x 10-13 M ⊙ yr-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 ± 50 pc to MV Lyr.