LITHIUM ABUNDANCES IN A FLUX-LIMITED SAMPLE OF GALACTIC CARBON STARS

Lithium abundances, or upper limits, have been derived for 161 galacti c carbon stars, selected from the Two Micron Sky Survey, using high re solution, high signal to noise ratio spectra and synthetic spectrum fi tting. Fourteen of these C-stars present surface lithium abundances [l og epsilon(Li) greater-than-or-equal-to 1.0] higher than theoretically expected during the AGB phase, but only three are super-rich lithium stars [log epsilon(Li) > 4], which confirms the scarce number of galac tic C-stars (approximately 2%) of this type. The average masses of the sample stars suggests the plume mixing, instead of the hot bottom bur ning mechanism, as the nucleosynthetic scenario for the production of lithium in these stars. However, the expected theoretical correlations among lithium abundances and C-12/C-13, C/O ratios do not show up. Th e lithium abundance distribution of the remaining stars shows a pronou nced peak at log epsilon(Li) almost-equal-to -0.5 suggesting, when com pared to those in M and SC stars, that no important lithium depletion occurs during the transition from M to C-star.