Chromospheric activity in cool stars and the lithium abundance

Abstract

A detailed analysis of the Ca II triplet lines lkern -4.1ptlower2pt char19 kern -0.8ptambdalkern -4.1ptlower2pt char19 kern -0.8ptambda8498, 8542, 8662 in 146 cool stars of all luminosities spanning a large range in metallicity has revealed that stars with similar temperature, luminosity and metallicity have different Ca II central depths due to different degrees of their chromospheric activity. Based on this idea, 14 stars in the sample have been identified as chromospherically more active than their counterparts with similar values of atmospheric parameters. In order to explore the interdependence between chromospheric activity, age and lithium abundance, CCD echelle spectra of the Li I line at 6707.8 Angstroms have been obtained at a spectral resolution of 0.35 Angstroms in these 14 active stars, 18 relatively inactive stars and another 17 stars randomly selected from the above sample. The analysis shows that although a few of the active stars are Li-rich, there does not exist a one-to-one correlation between Li abundance and chromospheric activity. There is almost an equal number of inactive stars which are Li rich. Otherwise, lithium depletions are large and there is a large spread in Li abundances in both active and inactive stars especially among giants and supergiants. For most of them, the abundance log N(Li) lies roughly between -0.3 to +0.7. A similar large range in Li abundances is found for giants not selected on the basis of chromospheric activity. The above observations suggest there are parameters besides the activity related ones controlling the lithium abundance in these stars.