Doppler images of the RS CVn binary II Pegasi during the years 1994–2002^⋆

¹ Department of Physics, University of Helsinki, PO Box 64, 00014 Helsinki, Finland
e-mail: marjaana.lindborg@helsinki.fi
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14882 Potsdam, Germany
³ Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden

Received: 13 June 2010
Accepted: 24 October 2010

Abstract

Aims. We publish 16 Doppler imaging temperature maps for the years 1994–2002 of the active RS CVn star II Peg. The six maps from 1999-2002 are based on previously unpublished observations. Through Doppler imaging we want to study the spot evolution of the star and in particular compare this with previous results showing a cyclic spot behaviour and persistent, active longitudes.

Methods. The observations were collected with the SOFIN spectrograph at the Nordic Optical Telescope. The temperature maps were calculated using a Doppler imaging code based on Tikhonov regularization.

Results. During 1994-2001, our results show a consistent trend in the derived longitudes of the principal and secondary temperature minima over time such that the magnetic structure appears to rotate somewhat more rapidly than the orbital period of this close binary. A sudden phase jump in the active region occurred between the observing seasons of 2001 and 2002. No clear trend over time is detected in the derived latitudes of the spots, indicating that the systematic motion could be related to the drift of the spot-generating mechanism rather than to differential rotation. The derived temperature maps are quite similar to the ones obtained earlier with different methods and the main differences occur in the spot latitudes and relative strength of the spot structures.

Conclusions. We observe both longitude and latitude shifts in the spot activity of II Peg. However, our results are not consistent with the periodic behaviour presented in previous studies.