Studies in RS canum venaticorum type stars a thesis submitted for the degree of Doctor of Philosophy in the faculty of science, Punjab University, Chandigarh S. Mohin [Ph.D Thesis]

Thesis Supervisor R. K. Kochhar

Doctor of Philosophy Indian Institute of Astrophysics, Bangalore\ 1992

It had been customary to divide variable stars into three classes: eruptive, pulsating, and eclipsing. It has recently been realized that there exists a fourth class of 'rotating variable stars' to which RS Canum Venaticorum systems belong. The most important characteristic of RS CVn systems in the optical region is the variable light curve arising from rotational modulation by spotted areas on the stellar photosphere. The present work was started with the aim of obtaining multiband photometric observations covering the entire phases of light curve for a few selected RS CVn stars and to use our database in conjunction with published
observations to numerically model the light curves with a view to deriving physical parameters. Though RS eVn characteristics were first detected in double-lined spectroscopic binaries, later many single-lined spectroscopic binaries
were found. We have selected two single-lined and two double-lined binaries for our investigation. All four are non-eclipsing close binaries: DM UMa and II Peg are single-lined, whereas V711 Tau and UX Ari are doublelined. All these objects are known to show HO:' as pure emission feature above the continuum at all times. This is a clear signature of chromospheric
activity. So it was decided to supplement the photometric data with H 0'. spectroscopy. The thesis has been divided into eight chapters.