METAL ABUNDANCES OF RED CLUMP STARS IN OPEN CLUSTERS: I. NGC 6819 1

Received; accepted – 2 – We present an analysis of high dispersion spectra (R ∼ 40, 000) of three red clump stars in the old open cluster NGC 6819. The spectra were obtained with SARG, the high dispersion spectrograph of the Telescopio Nazionale Galileo. The spectra were analyzed using both equivalent widths measured with an automatic procedure, and comparisons with synthetic spectra. NGC 6819 is found to be slightly metal-rich ([Fe/H]=+0.09 ± 0.03, internal error); there are no previous high resolution studies to compare with. Most element-to-element abundance ratios are close to solar; we find a slight excess of Si, and a significant Na overabundance. Our spectra can also be used to derive the interstellar reddening towards the cluster, by comparing the observed colours with those expected from line excitation: we derive E(B − V) = 0.14 ± 0.04, in agreement with the most recent estimate for this cluster. Subject headings: open clusters and associations: individual (NGC 6819) – stars: basic parameters – stars: stellar models – stars: abundances – techniques: spectroscopic 1Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Centro Galileo Galilei of the CNAA (Consorzio Nazionale per l’Astronomia e l’Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias – 3 – 1.