Doppler imaging of stellar surface structure. XVI. A time-series analysis of the moderately-rotating K1-giant sigma Geminorum
We present a simultaneous photometric and spectroscopic imaging analysis of the long-period RS CVn binary sigma Gem, covering 3.6 consecutive rotation cycles with high time resolution. From six overlapping but consecutive Doppler maps we trace the evolution of individual spots throughout the time range covered. All spots group either along a band at approximately +45 degrees latitude and a width of 30 degrees, or appear centered at the equator. No polar spot is detected. We did not find a conclusive migration pattern from the cross-correlation maps from one rotation to the next and attribute this to a masking effect of short-term spot changes.