[ITAL]Hubble Space Telescope[/ITAL] Observations of the Dwarf Nova WZ Sagittae: A Very Rapidly Rotating White Dwarf

Abstract

We present Hubble Space Telescope Goddard High-Resolution Spectrograph G140L spectra of the white dwarf in WZ Sge, exposed during quiescence. Our best-fitting synthetic spectra yield a rapidly rotating white dwarf with velocity Vrot sin i = 1200+ 300−400 km s-1, white dwarf effective temperature Twd = 14,800 K, the gravity log g = 8.0, and the chemical abundances relative to solar in number (with 3σ error bars) of C, 5.0+ 2.0−2.0; N, 3.0+ 1.0−1.0; and Si, <0.1. We also reexamined a previous Hubble Space Telescope Faint Object Spectrograph G130H spectrum reported by Sion and coworkers and obtained consistent values, but lower C and N abundances. We do not detect a measurable systematic shift in our observed spectra, presumably due to the extremely low mass of the companion.