A radial-velocity study of the dwarf nova RU Pegasi

Abstract

The spectrum of the dwarf nova RU Pegasi shows both hydrogen emission lines from an accretion disk surrounding the white dwarf primary and absorption lines from the late-type secondary star. A series of short exposure spectra of RU Peg are obtained, and the radial velocity variations of the absorption and emission lines are measured. An improved value for the orbital period of 0.3746 + or - 0.0002 d is obtained, and an apparent phase shift between the emission and absorption velocity curves is found. It is suggested that this phase shift and similar shifts found in several other systems may be due to an asymmetry in the emission distribution in the accretion disk.