Doppler imaging of stellar surface structure

XVI. A time-series analysis of the moderately-rotating K1-giant σ Geminorum

¹ Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest, Hungary e-mail: kovari@konkoly.hu; bartus@konkoly.hu
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: kstrassmeier, wasi, mweber@aip.de
³ Department of Physics, Brandon University, Brandon, Manitoba R7A 6A9, Canada e-mail: rice@BrandonU.ca

Corresponding author: K. G. Strassmeier, kstrassmeier@aip.de

Received: 9 June 2000
Accepted: 24 April 2001

Abstract

We present a simultaneous photometric and spectroscopic imaging analysis of the long-period RS CVn binary σ 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°latitude and a width of 30°, 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.