Chemical composition of photospheres in RS CVn stars

Tautvaisiene Grazina, grazina.tautvaisiene@tfai.vu.lt, Vilnius University, Lithuania
Barisevicius Gintaras, gintaras.barisevicius@tfai.vu.lt, Vilnius University, Lithuania
Berdyugina Svetlana, sveta@kis.uni-freiburg.de, Kiepenheuer Institut fur Sonnenphysik, Germany
Ilyin Ilya, ilyin@aip.de, Astrophysical Institute Potsdam, Germany
Chorniy Yuriy, yuriy.chorniy@tfai.vu.lt, Vilnius University

Abstract
RS CVn-type variables are remarkable due to large starspots, strong chromospheric plages, coronal X-ray and microwave emissions, as well as strong flares in the optical, radio and other spectral regions. The photometric brightness variation analysis, Doppler imaging and spectral line analysis of RS CVn stars indicate that starspots may cover up to about 40 percent of a stellar surface. The photospheric abundances of chemical elements in RS CVn-type stars are found to be peculiar and indicate a combined action of various physical processes related to activity. Peculiar elemental abundances were found in the coronal spectra of RS CVn stars as determined using cosmic satellites as well. In order to interpret the apparent abundance anomalies, we have started a detailed study of the photospheric abundances in RS CVn stars, and observed a sample of 28 such stars on the Nordic Optical Telescope. We investigate abundances of more than 20 chemical elements, including carbon isotopes, nitrogen and other mixing-sensitive species. In this presentation we present current results of the analysis, among which there are first evidences that extra-mixing processes may start acting in low-mass chromospherically active stars below the bump of the luminosity function of red giants.