We report abundance analysis for 6 M giant members of the old open cluster NGC6791, based on infrared spectroscopy (1.5-1.8 micron) at R=25,000, using the NIRSPEC spectrograph at the Keck II telescope. We find the iron abundance <[Fe/H]>= +0.35 +/- 0.02$, confirming the super solar metallicity of this cluster derived from optical medium-high resolution spectroscopy. We also measure C, O and other alpha element abundances, finding roughly solar [alpha/Fe] and <[C/Fe]> = -0.35. Our approach constrains [O/Fe] especially well, based on the measurement of a number of OH lines near 1.6micron; we find [O/Fe]=-0.07 +/-0.03. The Solar alpha enhancement is in contrast to the composition of similar stars in the Galactic bulge. We also find low 12C/13C~10, confirming the presence of extra-mixing processes during the red giant phase of evolution, up to super solar metallicities.
@article{arxiv.astro-ph/0604030,
title = {High resolution infrared spectroscopy of the old open cluster NGC6791},
author = {L. Origlia and E. Valenti and R. M. Rich and F. R. Ferraro},
journal= {arXiv preprint arXiv:astro-ph/0604030},
year = {2009}
}
Comments
14 pages, 3 figures, accepted for publication on ApJ