| Abstract : | Weak G-band stars or carbon-deficient giants are a rare class of G-K giants, whose spectra show a very weak or absent CH band at 4300A. Spectroscopic studies showed carbon abundances of these stars are under-abundant by about a factor of 20 when compared to the normal giants and highly enhanced in nitrogen abundance. Studies found high lithium enrichment in most of these stars. Weak G-band stars are claimed to be intermediate-mass stars with mass ranging from 2.5 Msun - 5 Msun. They are rare, as only about three dozen were known. Thus, we initiated a systematic survey among large spectroscopic databases, including LAMOST, for these peculiar stars among giants spanning disk metallicity. Our results increased the sample to three-fold and confirmed their rarity in our Galaxy. Spectra of some of these new carbon-deficient giants were obtained using the Himalayan Chandra Telescope. In this talk, I will discuss the newly discovered samples' properties, including their kinematics, Li and CNO abundances, masses, and evolutionary phases. Results show observations do not agree with standard stellar evolutionary models, indicating non-standard processes are required to explain the anomaly of light elements in these rare class of stars. The paper based on the above results is under review. |
