LITHIUM IN RS CVN BINARIES AND RELATED CHROMOSPHERICALLY ACTIVE STARS.2. SPECTRUM SYNTHESIS ANALYSIS

The results of the extensive survey of the Li I 6708 A line in RS CVn binaries and other chromospherically active stars carried out by Palla vicini et al. (1992) are reanalyzed using synthetic spectra. This allo ws us to obtain more accurate values of Li abundances and to separate the contributions of individual components of SB2 binaries. As a bypro duct, metallicities and rotational velocities are also obtained for al l stars in the sample. An effort is made to identify physically homoge neous subgroups of stars within the original sample, including: a) pre main sequence objects; b) young and/or warm stars on the mainsequence; c) cool evolved stars at T(eff) less-than-or-equal-to 5000 K (both me mbers of spectroscopic binaries and single K-type giants). We confirm that the latter group (which includes many catalogued RS CVn binaries) presents an excess Li abundance with respect to what typically observ ed in evolved stars of the same spectral type. However, the Li abundan ce is moderate (log n(Li) less-than-or-equal-to 1.5) and with no obvio us dependence on activity parameters such as rotation and chromospheri c emission. A significant amount of Lithium is observed only in a frac tion of these active cool stars and the presence of Li does not appear to be a characteristic property of RS CVn stars as a class. We argue, in agreement with Fekel et al. (1987), that the cool giants with exce ss Lithium might have evolved from main-sequence progenitors with shal low outer convective zones (M greater-than-or-equal-to 1.5 M.). Other possibilities discussed by Pallavicini et al. (1992), such as enhancem ent of the Li line in spotted stars, production of Li by spallation re actions in flares, and reduced rotationally-induced mixing in rapidly- rotating tidally-coupled binaries, cannot be excluded, but appear less likely. We find a significant metal deficiency for many stars in the sample, with no apparent correlation with Li abundance. However, the s pectral lines could be significantly affected by surface activity (spo ts and plages) and may not represent a true metal deficiency. Finally, we briefly comment on the possible role of active binaries in the Li enrichment of the Galaxy on the galactic evolutionary timescale.