Heavy-element abundances of the old open cluster NGC 6791

被引:69
作者
Peterson, RC [1 ]
Green, EM
机构
[1] Univ Calif Santa Cruz, Univ Calif Observ, Lick Observ, Santa Cruz, CA 95064 USA
[2] Univ Arizona, Steward Observ, Tucson, AZ 85721 USA
基金
美国国家科学基金会;
关键词
D O I
10.1086/311486
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The old open cluster NGC 6791 is believed to be more metal-rich than any other, yet several hot blue horizontal-branch (BHB) stars are probable members. We have performed an abundance analysis of the coolest BHB candidate, 2-17, whose proper motion and radial velocity both support cluster membership. its luminosity and its low rotational velocity, v sin i = 16 +/- 1 km s(-1), suggest that it is a BHB star rather than a very luminous blue straggler. We find an effective temperature T-eff = 7300 +/- 50 K, gravity log g = 3.6 +/- 0.3 dex, and an iron abundance more than twice solar, [Fe/H] = +0.4 +/- 0.1 dex. This result is free from the serious line blending and continuum suppression that hamper spectroscopic analyses of metal-rich giants. The Ca abundance is in the solar proportion with respect to iron, ruling out A-star peculiarities in 2-17. The relative abundances of C, O, and Al are nearly solar; mixing effects are probably small but not ruled out. The light elements Mg and Si are enhanced, N and Na especially so, as seen in metal-rich galaxies. NGC 6791 thus provides an excellent template for the study of the stellar content of metal-rich galactic systems. Both its abundances and its continued existence suggest that metal-rich systems might generally form in locally deep potential wells. Further study of its hot population should clarify the mechanisms responsible for producing hat stars in a metal-rich environment and thus assist the interpretation of the integrated light and the ultraviolet upturn in elliptical galaxies.
引用
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页码:L39 / L43
页数:5
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