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) 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 /sup 1/2C//sup 13/C ratio are correlated. Red giants with M> or approx. =1.3 M/sub sun/ show the predicted Li abundance and /sup 12/C//sup 13/C ratio. Giants with a high /sup 13/C abundance (/sup 12/C//sup 13/C< or approx. =15) show lower Li abundances. It is suggested that Li is a rough measure of a star's mass and that the high /sup 13/C stars are low-mass giants M< or approx. =1.3 M/sub sun/. The CN cycle is probably the source of the excess /sup 13/C. Spallation reactions cannot account for these abundances.Lithium must be produced by the weak G-band stars. The /sup 7/Be transport mechanism is the probable source of the Li. Meridional mixing in a red giant with a rapidly rotating core occurs too slowly for the /sup 7/Li to be transported to the cool envelope.