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

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 The six maps from 1999-2002 are based on previously unpublished observations.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 spotgenerating 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.

Doppler images of II Pegasi for 2004–2010

“…1) are very similar to those in our previous study (Lindborg et al 2011), the main difference being that the average temperature is now ∼100-150 K higher. This is a natural consequence of the revised stellar parameters in this study.…”

“…) also support the notion that the spot activity has decreased after 2002. A comparison with our earlier Doppler images (Lindborg et al 2011) also shows that the spots were more dominant in the images from 1994-2002 than during 2004-2010.…”

“…In a recent paper (Lindborg et al 2011), we published 16 temperature maps for the star II Peg during 1994-2002, revealing Several studies have found cyclic behaviour in II Peg. Rodonò et al (2000) analysed 25 years of photometry and reported cycles of 13.5, 9.5, and 6.8 years in the spot activity.…”

“…To make a more reliable comparison with our earlier Doppler images of 1994-2002(Lindborg et al 2011, we recalculated the images from 2002 using the new stellar parameters and model atmospheres. Since the earlier observations did not include the same wavelength regions as the present ones, we used the same wavelength regions as in the previous study.…”

“…The resulting maps are shown in the two uppermost left panels of Fig. 1. To study the evolution of the longitudinal spot distribution over time, we calculated average temperatures over all latitudes for each image for both our previous Doppler images (Lindborg et al 2011) and the present ones, represented in the left and right panels of Fig. 3.…”