Acoustic and magnetic wave heating in stars

III. The chromospheric emission–magnetic filling factor relation

¹ Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstr. 15, 69121 Heidelberg, Germany
² Warsaw University Observatory, Al. Ujazdowskie 4, 00478 Warszawa, Poland
³ Department of Physics, University of Texas at Arlington, Arlington, TX 76019, USA

Corresponding author: P. Ulmschneider, ulmschneider@ita.uni-heidelberg.de

Received: 5 November 2001
Accepted: 14 February 2002

Abstract

Theoretical chromospheric models described in the two previous papers of this series are used to study the relationship between the chromospheric emission and the filling factor. This theoretically determined relationship shows that the chromospheric emission flux in Ca II (H+K) is approximately proportional to the square root of the magnetic filling factor at the stellar surface. To relate the filling factor to stellar rotation rate, we compare the theoretical fluxes with observations of stars with known rotation period. The comparison shows that the Rossby number is probably a more appropriate measure of the rotation influence on activity of main-sequence stars than the rotation period. Our theoretical Mg II (h+k) and Ca II (H+K) emission fluxes are also found to be well correlated, which is in a good agreement with the observational data.