Name/Affiliation: Andreas Künstler (Leibniz-Institut für Astrophysik Potsdam (AIP), Germany)
Starspot evolution on the red giant star XX Triangulum
The importance of a spot decay timescale is that it relates to the magnetic diffusivity which itself is a driving parameter for the prediction of activity cycle periods of an aO-dynamo. Our current view of sunspot evolution prefers a linear area decay law dA(t)/dt = D. Furthermore it seems that the bigger the sunspot the stronger is its decay, as well as that the timescales of spot emergence are much shorter than for spot decay. To investigate the evolution of spots on other stars we need time-series of surface temperature maps (Doppler-Images). Since 2006 XX Triangulum (HD 12545) has been observed continuously with the STELLA Echelle Spectrograph. This red giant star of spectral class K0III is a RS CVn binary with a rotational and orbital period of 24 days. By now we have collected about 700 high-resolution spectra which cover 36 rotational periods. To reconstruct temperature maps of XX Tri we use our own Doppler-Imaging code iMap. During this timeframe we observe various spot phenomena such as spot decay and spot emergence, as well as spot fragmentation and spot merging, which allow us to determine area decay and growth rates. The longitudinal spot distribution enables us to detect active longitudes, which are in correlation to the appearence of the component star. Furthermore we determined a weak signal of differential rotation. We will present preliminary results of starspot evolution on XX Tri obtained from time-series Doppler-Images, including decay and growth rates of spot area, active longitudes, differential rotation and a so-called butterfly diagram.