Heavy-element abundances of the old open cluster NGC 6791

Ruth C. Peterson, Elizabeth M. Green

Research output: Contribution to journalArticlepeer-review

62 Scopus citations

Abstract

The old open cluster NGC 6791 is believed to be more metal-rich than any other, yet several hot blue horizontalbranch (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 Teff=7300±50 K, gravity log g=3.6±0.3 dex, and an iron abundance more than twice solar, [Fe/H]=10.4±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 hot stars in a metal-rich environment and thus assist the interpretation of the integrated light and the ultraviolet upturn in elliptical galaxies.

Original languageEnglish (US)
Pages (from-to)L39-L43
JournalAstrophysical Journal Letters
Volume502
Issue number1
DOIs
StatePublished - Jul 20 1998
Externally publishedYes

Keywords

  • Blue stragglers
  • Galaxies: stellar content
  • Open clusters and associations: individual (NGC 6791)
  • Stars: abundances
  • Stars: horizontal-branch

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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