A CH star in the globular cluster NGC 6426

Abstract

We report on the serendipitous discovery of a carbon star near the centre of the low-metallicity globular cluster NGC 6426. We determined its membership and chemical properties using medium-resolution spectra. The radial velocity of -159 km s-1 makes it a member of the cluster. We used photometric data from the literature and the COMARCS stellar atmospheric models to derive its luminosity, effective temperature, surface gravity, metallicity, and approximate C, N and O abundance ratios. According to these properties, we suggest that this star is a genuine carbon-rich low-metallicity asymptotic giant branch star. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.