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Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13

Behr, Bradford B. and Cohen, Judith G. and McCarthy, James K. and Djorgovski, S. George (1999) Striking Photospheric Abundance Anomalies in Blue Horizontal-Branch Stars in Globular Cluster M13. Astrophysical Journal, 517 (2). L135-L138. ISSN 0004-637X. doi:10.1086/312052.

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High-resolution optical spectra of 13 blue horizontal-branch stars in the globular cluster M13 show enormous deviations in element abundances from the expected cluster metallicity. In the hotter stars (T_(eff) > 12,000 K), helium is depleted by factors of 10-100 below solar, while iron is enhanced to 3 times the solar abundance, 2 orders of magnitude above the canonical metallicity of [Fe/H] ≃-1.5 dex for this globular cluster. Nitrogen, phosphorus, and chromium exhibit even more pronounced enhancements, and other metals are also mildly overabundant, with the exception of magnesium, which stays very near the expected cluster metallicity. These photospheric anomalies are most likely due to diffusion—the gravitational settling of helium and the radiative levitation of the other elements—in the stable radiative atmospheres of these hot stars. The effects of these mechanisms may have some impact on the photometric morphology of the cluster's horizontal branch and on estimates of its age and distance.

Item Type:Article
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URLURL TypeDescription Paper
Cohen, Judith G.0000-0002-8039-4673
Djorgovski, S. George0000-0002-0603-3087
Additional Information:© 1999 The American Astronomical Society. Received 1999 March 11; accepted 1999 March 29; published 1999 April 22. Based in large part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California. 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. Patrick Côté graciously provided assistance with many of the HIRES observations. Thanks also go to Manuela Zoccali, Elena Pancino, and Giampaolo Piotto for their reduction of the HST photometry and to Michael Lemke for introducing us to the LINFOR package and installing it locally. S. G. D. was supported, in part, by the Bressler Foundation. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Bressler FoundationUNSPECIFIED
Subject Keywords:globular clusters: general—globular clusters: individual (NGC 6205)—stars: abundances—stars: horizontal-branch
Issue or Number:2
Record Number:CaltechAUTHORS:20190528-140622271
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Official Citation:Bradford B. Behr et al 1999 ApJ 517 L135
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95828
Deposited By: Tony Diaz
Deposited On:28 May 2019 21:17
Last Modified:16 Nov 2021 17:16

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