Spectroscopy of the unique degenerate binary star LSI + 61 deg 303

IUE ultraviolet, and ground-based spectroscopic data are presented and discussed. The primary is a rapidly rotating B0 main-sequence star, with a stable shell. The radial velocities indicate binary motion in a 26.5-day orbit (in agreement with the radio flaring period), with a secondary of mass 1.1-1.5 solar masses. The broad Balmer emission appears to arise principally near the primary, and the line of sight is close to equatorial. These considerations bear on models involving X and gamma radiation from the system.