Spot activity of the RS Canum Venaticorum starσGeminorum

Abstract

Aims. We model the photometry of RS CVn star σ Geminorum to obtain new information on the changes of the surface starspot distribution, that is, activity cycles, differential rotation, and active longitudes. Methods. We used the previously published continuous period search (CPS) method to analyse V-band differential photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated Telescope at the Fairborn Observatory. The CPS method divides data into short subsets and then models the light-curves with Fourier-models of variable orders and provides estimates of the mean magnitude, amplitude, period, and light-curve minima. These light-curve parameters are then analysed for signs of activity cycles, differential rotation and active longitudes. Results. We confirm the presence of two previously found stable active longitudes, synchronised with the orbital period P orb = 19. d 60, and found eight events where the active longitudes are disrupted. The epochs of the primary light-curve minima rotate with a shorter period P min,1 = 19.d 47 than the orbital motion. If the variations in the photometric rotation period were to be caused by differential rotation, this would give a differential rotation coefficient of α ≥ 0.103. Conclusions. The presence of two slightly different periods of active regions may indicate a superposition of two dynamo modes, one stationary in the orbital frame and the other one propagating in the azimuthal direction. Our estimate of the differential rotation is much higher than previous results. However, simulations show that this may be caused by insufficient sampling in our data.

Antisolar differential rotation of the K1-giantσ Geminorum revisited

“…Indeed, this feature seems to be stable for much longer term than the range of our Doppler observations, affirming that tidal effects may organize preferred longitudes, as well as latitudes of activity in close binaries (cf. Kajatkari et al 2014 and see also the summary by Oláh 2007).…”

General Model for Light Curves of Chromospherically Active Binary Stars∗

“…Lehtinen et al (2011) formulated this method. It has been applied to the photometry of numerous stars (e.g., Hackman et al 2011;Kajatkari et al 2014;Lehtinen et al 2016), and it is therefore not described here in greater detail. We use only the results for independent and reliable data sets.…”

Periodicity in some light curves of the solar analogue V352 Canis Majoris

“…Here, we only briefly describe CPS, because we have already applied it to the photometry of several stars (Hackman et al , 2013Lehtinen et al 2012;Kajatkari et al 2014). CPS divides the data into segments (SEG) and datasets (SET).…”