Chromospheric activity in G and K giants and their rotation-activity relation


We obtained high-resolution CCD spectra of CaII H and K emission lines of 59 evolved stars of spectral type G and K and luminosity class III,III-IV, and IV. Our sample includes active stars like RS Cvn binaries but also active an inactive single stars. Whenever possible we determined absolute emission line surface fluxes from high-resolution spectra, to quantify the rotation-activity relation for evolved stars.

We find that the CaII surface fluxes from evolved stars scale linearly with stellar rotational velocity and that the flux from the cooler stars depends stronger upon rotation than the flux from the hotter stars, in agreement with previous findigs for main-sequence stars. However, large scatter indicates that rotational velocity might not be the only relevant parameter. We also present some evidence for the existence of a ‚basal‘ flux for evolved stars that scales approximately with the eigth power of the effective surface temperature

Authors: K. G. Strassmeier, G. Handler, E. Paunzen, M. Rauth

Department of Astronomy, University of Vienna
Türkenschanzstraße 17, A-1180 Wien, Austria

Keywords: stars: activity, stars: chromospheres, stars: latetype, stars: giant, mehtods: data analysis 
Published:Astronomy and Astrophysics, 281, pp.855-863, 1994.

Send offprint requests to K.G.Strassmeier.