A Star in the M31 Giant Stream: The Highest Negative Stellar Velocity Known

We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km s^-1. Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The evolutionary status of the star could be one of a post-main-sequence close binary, a symbiotic nova, or less likely, a post-asymptotic giant branch star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.