A Far-Ultraviolet Spectroscopic Analysis of BZ Ursae Majoris

Abstract

We present an analysis of the Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) far-ultraviolet snapshot spectrum of the dwarf nova BZ UMa taken during quiescence. We find that the flux continuum is consistent with that of a white dwarf atmosphere with a temperature of 15,000 K, a projected rotational velocity of 200 km/s, nonsolar abundances with enhanced N/C ratio, and a distance of ≈156 pc when assuming a white dwarf gravity of log g = 7.5. We also show that the hydrogen quasi-molecular satellite lines opacity affects the spectrum around λ ≈ 1300-1400 Å and has to be included to fine-tune the spectral modeling, this is self-consistent with the low stellar temperature we find.