Long-term photometry of RT lacertae: II. Further evidence for a circumstellar envelope and mass accretion

The light curves, obtained by the authors of the present paper during the p eriod 1978-1992, of the chromospherically active binary system RT Lac were examined. The average (B-V) colour indices were obtained and corrected for the interstellar extinction. Spectroscopic studies indicate that the less m assive component may be taken as G8. The light curve analysis indicates tha t the less massive, larger component fills its corresponding Roche lobe. Bo th photometric and spectroscopic observations compel one to draw a conclusi on that circumstellar matter does exist around the binary system. A colour excess caused by this matter is found to be 0.278 for B - V colour at mid-s econdary eclipse. On the basis of photometric colour indices alone, the com ponents of RT Lac are classified as G3-4 and G8. If we use the observed rad ial velocities of the less massive subgiant star from Ca II emission lines and from other optical lines we find for the mass of the more massive compo nent as 1.34-1.70 M.. This mass range corresponds to the main sequence late F stars. The common envelope hypothesis and mass function and also blendin g of the spectral lines of more massive component point out that it should be at most a late F type main sequence star.