Doppler images of II Pegasi for 2004–2010^⋆

¹ Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
e-mail: Thomas.Hackman@helsinki.fi
² Finnish Centre for Astronomy with ESO, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
³ Nordic Optical Telescope, 38700 Santa Cruz de la Palma, Spain
⁴ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14882 Potsdam, Germany
⁵ Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden

Received: 30 June 2011
Accepted: 15 December 2011

Abstract

Aims. We study the spot activity of II Peg during the years 2004–2010 to determine long- and short-term changes in the magnetic activity. In a previous study, we detected a persistent active longitude, as well as major changes in the spot configuration occurring on a timescale of shorter than a year. The main objective of this study is to determine whether the same phenomena persist in the star during these six years of spectroscopic monitoring.

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

Results. We present 12 new temperature maps that show spots distributed mainly over high and intermediate latitudes. In each image, 1–3 main active regions can be identified. The activity level of the star is clearly lower than during our previous study for the years 1994–2002. In contrast to the previous observations, we detect no clear drift of the active regions with respect to the rotation of the star.

Conclusions. Having shown a systematic longitudinal drift of the spot-generating mechanism during 1994–2002, the star has clearly switched to a low-activity state for 2004–2010, during which the spot locations appear more random over phase space. It could be that the star is near to a minimum of its activity cycle.