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Carbon Abundances of Faint Stars in M13: Evidence of Two Abundance-altering Mechanisms

Briley, Michael M. and Cohen, Judith G. and Stetson, Peter B. (2002) Carbon Abundances of Faint Stars in M13: Evidence of Two Abundance-altering Mechanisms. Astrophysical Journal, 579 (1). L17-L20. ISSN 0004-637X. doi:10.1086/345095.

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We present an analysis of CH band strengths in Keck Low-Resolution Imaging Spectrometer spectra of a sample of 81 stars in M13 within 2 mag of the main-sequence turnoff. The subgiants clearly exhibit a substantial (a factor of ~6) spread in [C/Fe]. Moreover, the bulk of the subgiants possess C abundances larger than those found among their more luminous counterparts. The turnoff stars themselves are too warm for appreciable CH formation, but the relatively small range in the observed CH band strength for stars just below the turnoff nevertheless translates into this same spread in [C/Fe]. Still fainter, the sample size is small, but the same range in [C/Fe] appears to be present. On the basis of these observations we suggest that a process external to the present stars has resulted in a substantial star-to-star dispersion in [C/Fe] (and possibly other light elements) among all stars in M13. In addition, the surface C abundances among the more luminous stars have been further modified by the operation of an internal deep-mixing mechanism during red giant branch ascent. The amplitude of the scatter we find in [C/Fe] at all luminosities may prove difficult to explain via accretion from intermediate-mass asymptotic giant branch stars as the external "polluting" mechanism.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Cohen, Judith G.0000-0002-8039-4673
Stetson, Peter B.0000-0001-6074-6830
Additional Information:© 2002 The American Astronomical Society. Received 2002 August 20; accepted 2002 September 26; published 2002 October 10. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The entire Keck/LRIS user communities owes a huge debt to Jerry Nelson, Gerry Smith, Bev Oke, and many other people who have worked to make the Keck Telescope and LRIS a reality and to operate and maintain the Keck Observatory. We are grateful to the W. M. Keck Foundation for the vision to fund the construction of the W. M. Keck Observatory.We wish to express our thanks to Roger Bell, whose SSG code was instrumental in this project. Partial support was provided by the National Science Foundation under grant AST 00-98489 to M. M. B. and grants AST 98-19614 and AST 02-05951 to J. G. C. and by the F. John Barlow professorship (M. M. B.).
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
NSFAST 00-98489
NSFAST 98-19614
NSFAST 02-05951
University of WisconsinUNSPECIFIED
Subject Keywords:globular clusters: general—globular clusters: individual (M13)—stars: abundances—stars: evolution
Issue or Number:1
Record Number:CaltechAUTHORS:20190522-092915815
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Official Citation:Michael M. Briley et al 2002 ApJ 579 L17
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95691
Deposited By: Tony Diaz
Deposited On:22 May 2019 22:04
Last Modified:16 Nov 2021 17:14

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