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The spread in CO absorption and effective temperature among the giants in omega Centauri

Persson, S. E. and Frogel, Jay A. and Cohen, J. G. and Aaronson, M. and Matthews, K. (1980) The spread in CO absorption and effective temperature among the giants in omega Centauri. Astrophysical Journal, 235 . pp. 452-469. ISSN 0004-637X. doi:10.1086/157648.

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Infrared photometric observations of 82 stars on the upper giant branch of ω Centauri are presented. The data show that ω Cen differs markedly from other globular clusters studied in the infrared in two respects. First, at a given V - K color, there is a wide spread in CO absorption (≳ 0.1 mag) in the 3 mag interval below the red giant tip; this range is approximately 5 times that found for other clusters. Second, at a given luminosity, V — K has a spread of up to 1 mag; this range is also much larger than that found for other clusters. The latter result leads us to conclude, in agreement with recent findings by other authors, that there are star-to-star variations in heavy-metal abundance within ω Cen of a factor of 30 or more. Comparison of the spread in CO absorption with that in V — K reveals two sequences of stars, one which has “enhanced” CO absorption and one which has “normal” CO absorption when compared to the run of CO with V — K among stars in other globular clusters. The proportion of stars having “enhanced” CO exceeds 50%. Many of the strong CN stars in the cluster also have “enhanced” CO. Explanations for the origin of these sequences which involve primordial abundance variations as well as mixing phenomena are discussed briefly. Implications for the identification of the “second parameter” as the CNO abundance are also discussed. Effective temperatures and bolometric luminosities are given for the stars.

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Cohen, J. G.0000-0002-8039-4673
Additional Information:© American Astronomical Society • Provided by the NASA Astrophysics Data System. Received 1979 April 9; accepted 1979 July 31. We are grateful to M. Clark, G. Forrester, A. Guerra, L. Papic, and F. Peralta for their help with the equipment and observations at Las Campanas and to J. Baldwin and J. Rios for their help at CTIO. We thank J. Baldwin, J. Elias, B. Lasker, G. Neugebauer, F. Schweizer, and R. Zinn for discussions, and P. Gilman, N. Newton, and J. Bedke for help in preparing the manuscript. This work was supported in part by NSF grant 76-22676. The Hale Observatories are operated jointly by the Carnegie Institution of Washington and the California Institute of Technology. Cerro Tololo Inter-American Observatory is supported by the National Science Foundation under contract AST 78-27879.
Funding AgencyGrant Number
NSFAST 76-22676
NSFAST 78-27879
Subject Keywords:clusters: globular — stars: abundances — stars: evolution — stars: late-type
Record Number:CaltechAUTHORS:20190529-161905266
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95931
Deposited By: George Porter
Deposited On:31 May 2019 15:27
Last Modified:16 Nov 2021 17:16

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