Metallicities of two distant globular clusters from spectra of moderate dispersion.
WACHTER S., WALLERSTEIN G., BROWN J.A. and OKE J.B.
Abstract (from CDS):
We have used model atmospheres and spectrum synthesis to analyze medium resolution, moderate signal-to-noise, blue spectra of three stars in each of the globular clusters NGC 7006 and NGC 6229 for metallicity and carbon abundance. Both clusters are known to have intermediate metallicity, but NGC 7006 has a reddish horizontal branch, while NGC 6229 has a blue horizontal branch. We find that [MMH]=-1.6 for NGC 7006 and [MMH]=-1.4 for NGC 6229, with uncertainties near ±0.1. In NGC 7006 carbon is depleted, presumably by CN cycling, so that [CMFe]=-0.71. Our [C/Fe] ratio, as derived for stars with Teff∼4200 K, agrees with the [C/Fe] ratio found by Friel et al. for stars with Teff between 4500 and 4700 K. This shows that the stars in NGC 7006 have not suffered additional mixing as they advance up the giant branch from 4700 K to the red giant tip. For NGC 6229 we derive [CMFe]=-0.56. We find evidence for a scatter in [C/Fe], indicating differing degrees of carbon depletion from star to star.
Galaxy: Halo - Galaxy: Globular Clusters: Individual: NGC Number: NGC 6229 - Galaxy: Globular Clusters: Individual: NGC Number: NGC 7006 - Stars: Abundances