Doppler images of II Pegasi for 2004–2010

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.

Multiperiodicity, modulations and flip-flops in variable star light curves

“…In some previous studies of II Peg (e.g. Berdyugina et al 1999), indications of flip flops were reported that the abrupt activity jumps from one longitude to another, separated roughly by 180 degrees, but the results of Lindborg et al (2011) and Hackman et al (2012) did not support this interpretation.…”

“…Berdyugina et al 1998aBerdyugina et al , 1999Gu et al 2003;Lindborg et al 2011;Hackman et al 2012) and magnetic field maps have been published (Kochukhov et al 2013;Carroll et al 2007Carroll et al , 2009). The star's photometric light curves have also been intensively studied with time-series analysis and spot-modeling methods (see e.g.…”

Magnetic field topology of the RS CVn star II Pegasi

“…Other studies targeted II Peg with high-resolution spectroscopic observations with the goal to constrain the spot temperatures using TiO absorption bands (O'Neal et al 1998;Berdyugina et al 1998b) and to analyse configurations of the surface temperature inhomogeneities with the Doppler imaging technique (Berdyugina et al 1998a;Gu et al 2003;Lindborg et al 2011;Hackman et al 2012). Early DI images corresponding to the period between 1994 and 2002 suggested persistent presence of a pair of active longitudes and showed major changes in the surface structure on a time-scale of less than a year (Berdyugina et al 1998a(Berdyugina et al , 1999Lindborg et al 2011).…”

“…Early DI images corresponding to the period between 1994 and 2002 suggested persistent presence of a pair of active longitudes and showed major changes in the surface structure on a time-scale of less than a year (Berdyugina et al 1998a(Berdyugina et al , 1999Lindborg et al 2011). More recent DI maps covering the years from 2004 to 2010 revealed the star entering a low-activity state characterised by a more random distribution of cool spots (Hackman et al 2012).…”

“…In this paper we present a comprehensive analysis of these polarisation data, focusing on the selfconsistent ZDI mapping of stellar magnetic field topology. The accompanying study by Hackman et al (2012) obtained temperature maps from the same SOFIN Stokes I spectra. Preliminary attempts to map the magnetic field geometry of II Peg, using about 10% of the spectropolarimetric data analysed here, were presented first by Carroll et al (2007), and then by Carroll et al (2009b) and .…”