Study of FK Comae Berenices

VII. Correlating photospheric and chromospheric activity^{⋆,⋆⋆,⋆⋆⋆}

¹ Konkoly Observatory, MTA CSFK, H-1121 Budapest, Konkoly Thege M. út 15–17, Hungary
e-mail: vidakris@konkoly.hu
² Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
e-mail: heidi.h.korhonen@utu.fi
³ Centre for Star and Planet Formation, Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark
⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁵ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
⁶ Department of Physics, PO Box 64, 00014 University of Helsinki, Finland

Received: 10 March 2015
Accepted: 21 May 2015

Abstract

Aims. We study the connection between the chromospheric and photospheric behaviour of the active late-type star FK Comae.

Methods. We use spot temperature modelling, light curve inversion based on narrow- and wide-band photometric measurements, Hα observations from 1997−2010, and Doppler maps from 2004−2010 to compare the behaviour of chromospheric and photospheric features.

Results. Investigating low-resolution Hα spectra, we find that the changes in the chromosphere seem to happen mainly on a time scale longer than a few hours, but shorter variations are also observed. According to the Hα measurements, prominences are often found in the chromosphere that reach to more than a stellar radius and are stable for weeks, and they seem to be often, but not always connected to dark photospheric spots. The rotational modulation of the Hα emission typically seems to be anticorrelated with the light curve, but we did not find convincing evidence of a clear connection in the long-term trends of the Hα emission and the brightness of the star. In addition, FK Com seems to be in an unusually quiet state in 2009−2010 with very little chromospheric activity and low spot contrast, which might indicate the long-term decrease in activity.