Lithium abundance and activity for 57 RS CVn systems

Abstract

The high resolution (0.049–0.145Å) and high signal-to-noise ratio (100–600) Reticon and CCD spectra of 57 binaries of the RS CVn type were obtained with the coudé spectrograph of the McDonald Observatory 2.1m telescope and the Yunnan Observatory 1m telescope for an analysis of the correlation between Li abundance and chromospheric activity. The Li abundance of 57 RS CVn systems, which include 76 detected components, has been determined through the observed equivalent widths of the Li doublet (6707.761Å + 6707.912Å) and Kurucz's model atmospheres. By the method of the comprehensive analysis of the atmospheric model the abundances of [Fe/H], [Ti/Fe] and logN(Li) have been calculated for 10 of the above mentioned binaries. We have made statistical analysis of the correlations between the lithium abundance and the effective temperature T eff as well as the projected rotational velocity, v sin i. The results show that the Li abundance tends to decrease with the drop of T eff. On the other hand, the Li abundance has a tendency to decrease with the increase of v sin i, but the dispersion of this correlation is very large. In particular, in the range of v sin i < 25km/sec we may say that no correlation exists at all. Besides, a statistical analysis shows that there is no evident relation between the Li abundance of 57 binaries of the RS CVn type and the level of activity. However, it is worthwhile to note that the Li abundances of the cold components in 7 binary systems during the period of strong activity are lower than those of the less active hot components. The opposite case has never been found.