Spectroscopic charaterization of FHLC stars from the Hamburg/ESO survey and a newly found HdC star

Abstract

The sample of candidate faint high latitude carbon (FHLC) stars chosen from the Hamburg/ESO survey is a potential source to search for objects of rare types. From medium resolution spectral analyses of about 250 objects from this sample, the object HE 1015-2050, was found to be a hydrogen-deficient carbon (HdC) star. Apart from U Aquarii, HE 1015-2050 is the only example, till now, of a Galactic cool HdC star that is characterized by strong spectral features of light s-process element Sr, and weak features of heavy s-process elements such as Ba. This object, with its enhanced carbon and hydrogen-deficiency, together with anomalous s-process spectral features, poses a challenge as far as the understanding of its formation mechanism is concerned. We discuss possible mechanisms for its formation in the framework of existing scenarios of HdC star formation.