Astron. Astrophys. Suppl. Ser. 137, 217-221

Photometry and spectroscopy of the RS CVn system $\sigma$ Geminorum

X.B. Zhang^1,2 and R.X. Zhang¹

Send offprint request: X.B. Zhang

1 - Beijing Astronomical Observatory, Chinese Academy of Sciences, Bejing 100101, China
e-mail: xzhang@class1.bao.ac.cn
2 - Chinese Academy of Sciences-Peking University joint Beijing Astrophysical Center, Beijing 100871, China

Received July 22; accepted August 31, 1998

Abstract:

We present new UBV photoelectric photometry and high-resolution H$_{\alpha}$ spectroscopy of the RS CVn system $\sigma$ Gem made in 1993-1994. A brief photometric analysis for the new light curves is carried out using the Wilson-Devinney method with spot approximation based on the Roche model. The result suggests the probable presence of two cool spots on the K1 III primary around the phases of $\phi =0.6$ and $\phi=0.9$. The spot activity is discussed in connection with the chromospheric H$_{\alpha}$ emission. The enhanced H$_{\alpha}$ core emission is found to vary with phase and shows distinct anti-correlation with the spot regions. It may be an indication for the existence of plage regions on $\sigma$ Gem.

Key words: stars: $\sigma$ Gem; activity -- binaries: close