Spot activity of the RS CVn star σ Geminorum

Abstract

We model the photometry of RS CVn star $\sigma$ Geminorum to obtain new information on the changes of the surface starspot distribution, i.e., activity cycles, differential rotation and active longitudes. We use the previously published Continuous Periods Search-method (CPS) 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. We confirm the presence of two previously found stable active longitudes, synchronised with the orbital period $P_{\mathrm{orb}}=19.60$d and find eight events where the active longitudes are disrupted. The epochs of the primary light curve minima rotate with a shorter period $P_{\min ,1}=19.47$d 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 $\alpha \ge 0.103$. 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 can be caused by insufficient sampling in our data.

arXiv comment10 pages, 6 figures. Submitted to A&A

References in corpus (6)

• Flip-flops of FK Comae Berenices
• Azimuthal dynamo wave in spherical shell convection
• Spot activity of LQ Hya from photometry between 1988 and 2011
• The continuous period search method and its application to the young solar analogue HD 116956
• Investigating variation of latitudinal stellar spot rotation and its relation to the real stellar surface rotation
• Surface velocity network with anti-solar differential rotation on the active K-giant $\sigma$ Geminorum

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• General Model for Light curves of Chromospherically Active Binary Stars
• Observing the changing surface structures of the active K giant sigma Gem with SONG
• Periodicity in some light curves of the solar analogue V352 CMa
• Time series analysis of long-term photometry of BM Canum Venaticorum
• Spectroscopic and photometric analysis of 21 chromospherically active variables: activity cycles and differential rotation
• Characterising the stellar differential rotation based on largest-spot statistics from ground-based photometry