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

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

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...281..855s&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 281, no. 3, p. 855-863

Astronomy and Astrophysics

Astrophysics

48

Chromosphere, G Stars, Giant Stars, K Stars, Stellar Activity, Stellar Rotation, Stellar Spectra, Astronomical Spectroscopy, Calcium, Emission Spectra, H Lines, K Lines, Stellar Temperature

Scientific paper

We obtained high-resolution CCD spectra of Ca II 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 and inactive single stars. Whenever possible we determine absolute emission line surface fluxes and use them, supplemented by previously published fluxes from high-resolution spectra, to quantify the rotation-activity relation for evolved stars. We find that the Ca II 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 findings 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 eight power of the effective surface temperature.

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