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Published January 10, 2000 | Published + Accepted Version
Journal Article Open

A New Spin on the Problem of Horizontal‐Branch Gaps: Stellar Rotation along the Blue Horizontal Branch of Globular Cluster M13


We have determined the projected rotational velocities of 13 blue horizontal-branch (BHB) stars in the globular cluster M13 via rotational broadening of metal absorption lines. Our sample spans the photometric gap observed in the horizontal-branch distribution at T_(eff) 11,000 K and reveals a pronounced difference in stellar rotation on either side of this feature—blueward of the gap, all the stars show modest rotations, v sin i < 10 km s^(-1), while to the red side of the gap, we confirm the more rapidly rotating population (v sin i ≃ 40 km s^(-1)) previously observed by R. C. Peterson and coworkers. Taken together with these prior results, our measurements indicate that a star's rotation is indeed related to its location along the HB, although the mechanism behind this correlation remains unknown. We explore possible connections between stellar rotation and mass-loss mechanisms which influence the photometric morphology of globular cluster HBs.

Additional Information

© 2000 The American Astronomical Society. Received 1999 May 3; accepted 1999 August 24. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. These observations would not have been feasible without the HIRES spectrograph and the Keck I telescope. We are indebted to Jerry Nelson, Gerry Smith, Steve Vogt, and many others for making such marvelous machines; to the W. M. Keck Foundation for making it happen; and to a bevy of Keck observing assistants for making them work. S. G. D. was supported, in part, by the Bressler Foundation, and STScI grant GO-7470. J. G. C. acknowledges support by NSF grant AST-9819614. P. C. gratefully acknowledges support provided by the Sherman M. Fairchild Foundation. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.

Attached Files

Published - Behr_2000_ApJ_528_849.pdf

Accepted Version - 9907211.pdf


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