AAS 203rd Meeting, January 2004
Session 112 The Milky Way and Its Environs
Poster, Thursday, January 8, 2004, 9:20am-4:00pm, Grand Hall

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[112.23] Rotation in Metal-poor Field Red Giant and Red Horizontal Branch Stars

B. W. Carney (University of North Carolina), D. W. Latham (Center for Astrophysics), J. B. Laird (Bowling Green State University), J. A. Morse (Arizona State University)

We have previously reported (Carney et al., AJ, 125,293, 2003) results of radial velocity monitoring of 91 metal-poor field red giant (RGB) and red horizontal branch (RHB) stars. We also estimated rotational velocities, finding significant rotation (> 8.5 km sec-1) for tidally-linked binaries plus a few non-binary but highly luminous red giants. We proposed that the rotation of the latter stars may have been caused by absorption of a planet as the star expanded to its current large radius. We also found 6 of the 15 RHB stars showed similarly large rotational velocities.

We have begun observing 43 additional RGB and RHB stars. Velocity coverage is less than one year for 10 stars, about one year for 29 stars, and exceeds 18 years for the remaining 4 stars. Only one of the RGB stars with MV < -1.4 shows vrot sin i > 10 km sec-1. It does not appear to be in a close binary system. Three of the five RHB stars show similarly high values of rotation. We thus confirm our earlier finding that a modest fraction of the most luminous metal-poor field RGB stars (and only the most luminous ones) show significant rotation, independent of stellar companions, and that of order half of the metal-poor field RHB stars show similarly high rotational velocities.

This work has been supported in part by NSF grants AST-9988156 and AST-0305431 to UNC.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.