A Runaway Red Supergiant in M31

Kate Anne Evans (1,2) and Philip Massey (1,3)

1 - Lowell Observatory, Flagstaff, AZ 86001;
2 - REU participant, currently at the California Institute of Technology, Pasadena, CA 91125;
3 - Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011

A significant percentage of OB stars are runaways, so we should expect a similar percentage of their evolved descendants to also be runaways. However, recognizing such stars presents its own set of challenges, as these older, more evolved stars will have drifted further from their birthplace, and thus their velocities might not be obviously peculiar. Several Galactic red supergiants (RSGs) have been described as likely runaways, based upon the existence of bow shocks, including Betelgeuse. Here we announce the discovery of a runaway RSG in M31, based upon a 300 km/s discrepancy with M31's kinematics. The star is found about 21' (4.6 kpc) from the plane of the disk, but this separation is consistent with its velocity and likely age (~10 Myr). The star, J004330.06+405258.4, is an M2 I, with an absolute visual magnitude of -5.7, log(L/L(solar))=4.76, an effective temperature of 3700 K, and an inferred mass of 12-15 solar masses. The star may be a high-mass analog of the hypervelocity stars, given that its peculiar space velocity is probably 400-450 km/s, comparable to the escape speed from M31's disk.

Reference: Astronomical Journal (in press)
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1509.07251


Email: kevans@caltech.edu