Abundances of four open clusters from solar stars

G. Pace, L. Pasquini, P. François

Abstract

Aims. We present the abundance measurements of several elements (Fe, Ca, Na, Ni,  Ti, Al, Cr, Si) for 20 solar–type stars belonging to four Galactic open clusters: NGC  3680, IC 4651, Praesepe, and M 67. Oxygen abundances were in addition measured for most stars in each cluster apart from IC 4651. For NGC 3680, accurate abundance  determinations using high–resolution spectra covering a large spectral domain are computed for the first time.
Methods. We used UVES high–resolution, high signal–to–noise (S/N) ratio spectra and  performed a differential analysis with respect to the sun, by measuring equivalent widths and assuming LTE.
Results. The most surprising result is a measurement of significant supersolar  metallicity for Praesepe ([Fe/H]=0.27±0.10). As for the other clusters, we confirm a  supersolar metallicity for IC 4651 ([Fe/H]=0.12±0.05), a solar metallicity for M 67  ([Fe/H]=0.03±0.04) and a slight subsolar metallicity for NGC 3680  ([Fe/H]=-0.04±0.03). We find that the abundance ratios of almost all elements are solar, with the notable exception of oxygen in NGC 3680 and Praesepe, supersolar in  the former cluster ([O/Fe]=0.2±0.05) and as low as [O/Fe]=-0.4±0.1 in the latter.  Observations of several objects per cluster is required to obtain robust results, especially for those elements with a limited number of suitable lines.

Astronomy and Astrophysics
Volume 489, Page 403
October 2008

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