Lithium in late-type giants. I - G and K giants

Lithium abundances for about 50 G and K giants have been derived from new high-resolution, low-noise spectra by spectrum synthesis. Ca abundances obtained from the 6798 A Ca I line are well correlated with the Fe/H forbidden line abundance given by published narrow-band photometry. This correlation is strong evidence that the Ca and, therefore, the Li abundances are free from large systematic errors. The Li abundance and the C-12/C-13 ratio are correlated. Red giants with mass not less than 1.3 solar mass show the predicted Li abundance and C-12/C-13 ratio. Giants with a high C-13 abundance show lower Li abundances. It is suggested that Li is a rough measure of a star's mass and that the high C-13 stars are low-mass giants with mass not greater than 1.3 solar mass. The CN cycle is probably the source of the excess C-13. Spallation reactions cannot account for these abundances.