Searching for chemical signatures of multiple stellar populations in the old, massive open cluster NGC 6791

Journal Article · Thu Nov 20 04:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/796/1/68· OSTI ID:22369988

Bragaglia, Angela; Carretta, Eugenio ^[1]; Sneden, Christopher ^[2]; Gratton, Raffaele G.; Lucatello, Sara ^[3]; Bernath, Peter F. ^[4]; Brooke, James S. A.

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1. INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
2. Department of Astronomy and McDonald Observatory, C1400, University of Texas, Austin, TX 78712 (United States)
3. INAF-Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, I-35122 Padova (Italy)
4. Department of Chemistry and Biochemistry, Old Dominion University, 4541 Hampton Boulevard, Norfolk, VA 23529-0126 (United States)

Galactic open and globular clusters (OCs, GCs) appear to inhabit separate regions of the age-mass plane. However, the transition between them is not easily defined because there is some overlap between high-mass, old OCs and low-mass, young GCs. We are exploring the possibility of a clear-cut separation between OCs and GCs using an abundance feature that has been found so far only in GCs: (anti)correlations between light elements. Among the coupled abundance trends, the Na-O anticorrelation is the most widely studied. These anticorrelations are the signature of self-enrichment, i.e., of a formation mechanism that implies multiple generations of stars. Here we concentrate on the old, massive, metal-rich OC NGC 6791. We analyzed archival Keck/HIRES spectra of 15 NGC 6791 main-sequence turnoff and evolved stars, concentrating on the derivation of C, N, O, and Na abundances. We also used WIYN/Hydra spectra of 21 evolved stars (one is in common). Given the spectral complexity of the very metal-rich NGC 6791 stars, we employed spectrum synthesis to measure most of the abundances. We confirmed the cluster super-solar metallicity and abundances of Ca and Ni that have been derived in past studies. More importantly, we did not detect any significant star-to-star abundance dispersion in C, N, O, and Na. Based on the absence of a clear Na-O anticorrelation, NGC 6791 can still be considered a true OC, hosting a single generation of stars and not a low-mass GC.

• OSTI ID: 22369988
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 796; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CALCIUM
CORRELATIONS
DISPERSIONS
ELEMENT ABUNDANCE
GALAXY CLUSTERS
MASS
METALLICITY
METALS
NICKEL
SPECTRA
STARS
SYNTHESIS
VISIBLE RADIATION