Lithium abundances in carbon stars

Abstract

High-dispersion, high SNR ratio spectra near 6707 A have provided Li abundances for 29 cool carbon stars. For the carbon stars, with the exception of the J star WZ Cas, the Li abundance ranges from log epsilon(Li) = -0.6 to -1.7 and is uncorrelated with the C-12/C-13, C/O and other abundance ratios, and the effective temperature. The Li abundances are on average lower than found for M giants. This difference may be due to a systematic underestimate of the carbon stars' effective temperatures by 200-400 K. It is possible that Li may be destroyed at the base of an asymptotic giant branch star's convective envelope. When the base temperature increases substantially, Li may be produced by the B-7 transport mechanism, as in the super Li-rich SC (J-type) star WZ Cas with log epsilon(Li) = 6.5.