Lithium in Rs-Canum Binaries and Related Chromospherically Active Stars - Part Two - Spectrum Synthesis Analysis

Details Lithium in Rs-Canum Binaries and Related Chromospherically Active Stars - Part Two - Spectrum Synthesis Analysis Lithium in Rs-Canum Binaries and Related Chromospherically Active Stars - Part Two - Spectrum Synthesis Analysis

Jun 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...273..194r&link_type=abstract

Astronomy and Astrophysics, Vol.273, NO. 1/JUNI, P. 194, 1993

Astronomy and Astrophysics

Astrophysics

104

Stars: Abundances, Stars: Activity, Stars: Atmospheres

Scientific paper

The results of the extensive survey of the Li I 6708 Å line in RS CVn binaries and other chromospherically active stars carried out by Pallavicini et al. (1992) are reanalyzed using synthetic spectra. This allows us to obtain more accurate values of Li abundances and to separate the contributions of individual components of 5B2 binaries. As a byproduct, metallicities and rotational velocities are also obtained for all stars in the sample. An effort is made to identify physically homogeneous subgroups of stars within the original sample, including: a) pre-main sequence objects; b) young and/or warm stars on the main- sequence; c) cool evolved stars at Teff ≤ 5000 K (both members 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 observed in evolved stars of the same spectral type. However, the Li abundance is moderate (log n(Li) ≤ 1.5) and with no obvious dependence on activity parameters such as rotation and chromospheric emission. A significant amount of Lithium is observed only in a fraction 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 excess Lithium - might have evolved from main-sequence progenitors with shallow outer convective zones (M ≥ 1.5 Msun). Other possibilities discussed by Pallavicini et al. (1992), such as enhancement of the Li line in spotted stars, production of Li by spallation reactions 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 spectral lines could be significantly affected by surface activity (spots 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.

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