5 Summary

We made new UBV photoelectric photometry and high resolution H$_{\alpha}$spectroscopy of the chromospheric active binary system $\sigma$ Gem in 1993-1994. The analysis of the light curves and the H$_{\alpha}$ spectra yield the following results:

(1) The light curve migrated steadily and the distortion wave varied comparing to the previous observations, though the measurements show a considerable scatter. A brief photometric analysis, carried out using the Wilson-Devinney method, suggests two cool spots on the primary component of $\sigma$ Gem around phases of 0.6 and 0.9 apart from additional spots causing the general dimming of the star.

(2) In connection with the photometric observation, the H$_{\alpha}$spetctroscopy of $\sigma$ Gem is analyzed. It is found that the core of the H$_{\alpha}$ profile is varying with phase and time. The near to simultaneous photometry and spectroscopy enable us to find that the enhanced H$_{\alpha}$core emissions show distinct anti-correlation with spot regions. Our study suggests that there may be some plage-type regions around the maximum light, where the enhanced H$_{\alpha}$ emission comes from.

Acknowledgements

This work is a contribution to the memory of our honoured Professor Zhai Disheng. He had been concerned with this work until his passing away. The authors would like to thank the Natural Science Foundation of China for financial support. Thanks are also due to Dr. J.X. Wang for his most helpful discussions.