2014/12/31 by Ann Merchant Boesgaard, Michael G. Lum, Constantine P. Deliyannis · 31 citations
Physics and Astronomy · Social Sciences · #Astronomy and Astrophysical Research #Educational Leadership and Practices #Metallicity #Open cluster #Population #Spectral line #Star cluster #Stars #Stellar evolution #Stellar population #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/799/2/202
published in The Astrophysical Journal 799(2), 202 (IOP Publishing) · Accepted by The Astrophysical Journal 14 pages, 10 figures, 10 tables
arxiv created 2015/01/17 · openalex publication_date 2015/01/30 · arxiv updated 2015/06/23 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The study of star clusters has advanced our understanding of stellar evolution, Galactic chemical evolution, and nucleosynthesis. Here we investigate the composition of turn-off stars in the intriguing open cluster, NGC 6791, which is old, but super-metal-rich with high-resolution ( R = 46,000) Keck/HIRES spectra. We find [Fe/H] = +0.30 ± 0.02 from measurements of some 40 unblended, unsaturated lines of both Fe i and Fe ii in eight turn-off stars. Our O abundances come from the O i triplet near 7774 Å and we perform a differential analysis relative to the Sun from our Lunar spectrum also obtained with Keck/HIRES. The O results are corrected for small nLTE effects. We find consistent ratios of [O/Fe] n with a mean of −0.06 ± 0.02. This is low with respect to field stars that are also both old and metal-rich and continue the trend of decreasing [O/Fe] with increasing [Fe/H]. The small range in our oxygen abundances is consistent with a single population of stars. Our results for the alpha elements [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe] are near solar and compare well with those of the old, metal-rich field stars. The two Fe-peak elements, Cr and Ni, are consistent with Fe. These turn-off-star abundances provide benchmark abundances to investigate whether there are any observable abundance differences with the giants that might arise from nuclear-burning and dredge-up processes. Determinations of upper limits were found for Li by spectrum synthesis and are consistent with the upper limits in similar stars in the relatively old, super-metal-rich cluster NGC 6253. Our results support the prediction from standard theory that higher-metallicity stars deplete more Li. Probably no stars in NGC 6791 have retained their initial Li.