| Abstract: | Hydrogen-deficient carbon stars (HdCs), as the name suggests, are characterized by atmospheres that are poor in hydrogen and rich in carbon. When compared to a normal star, HdCs' optical spectra show very weak presence or absence of hydrogen Balmer lines for their effective temperatures. The process that is responsible for the origin of these stars, which transforms a normal star into a H-poor HdC star, is still a mystery. For several decades, there were just about 5 known HdCs. However, note that there exists yet another class of hydrogen-deficient stars known as R Coronae Borealis stars (RCBs). Unlike HdCs, RCBs exhibit remarkable photometric variability by undergoing unpredictable light decline (up to about 9 mag in visual). It is heartening that a recent survey has reported about 27 new HdCs, a sixfold increase in their number than the earlier known (Tisserand et al. 2022). Warner (1967) provides the abundances of five earlier known HdC stars but with outdated observational methods and abundance analysis techniques. And, there are no measurements available for the elemental abundances of newly discovered HdC stars to date. Detailed abundance analysis serves as a crucial observational constraint on theoretical models concerning the formation and evolution of stars. In this regard, we conducted a fine abundance analysis of a new warm HdC star, A980 (2MASS 18113561+0154326), using a high-resolution spectrum obtained from Hanle Echelle Spectrograph (HESP), mounted on 2-m Himalayan Chandra Telescope (HCT) in Hanle, India. I will present the findings from our analysis which includes (a) a confirmation of A980 as an Extreme Helium (EHe) star that was earlier classified as an HdC star, (b) discovery of germanium transitions and its enhancement in A980, a cool EHe, suggesting synthesis of germanium in A980’s evolution, and (c) strongest s-process enhancement measured in A980 among the other cool EHes. |
