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

TL;DR

This paper reports the discovery of a star in M31 with an unprecedented negative radial velocity of -780 km/s, likely belonging to the Andromeda Giant Stream, and discusses its possible evolutionary states.

Contribution

It identifies a star with the highest negative stellar velocity in M31 and analyzes its spectral properties and potential membership in the Giant Stream.

Findings

Star B030D has a radial velocity of -780 km/s.

The star is an F supergiant with a circumstellar shell.

Its velocity suggests membership in the Andromeda Giant Stream.

Abstract

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. 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-mainsequence close binary, a symbiotic nova, or less likely, a post-AGB star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.