4 Conclusions

A comparison of the presently derived parameters with those of [7, Giuricin & Mardirossian (1981)] as well as [18, Niarchos et al. (1998)] indicate that YY CMi is an A type W UMa contact system.

From the present analysis, we obtained a mass ratio of q=0.89 which differs from the mass-ratio of 0.8 derived by [7, Giuricin & Mardirossian (1981)] and 0.65 derived by Abhyankar but agrees with that found by [18, Niarchos et al. (1998)]. This discrepancy in the values of the q may be attributed to the different methods adopted in the analysis. The UBV light curves of YY CMi show an O'Connell effect which suggests that there might be some source responsible for it. Like [18, Niarchos et al. (1998)] we attribute this effect to the spot activity on the surface of the cool secondary component. We have already noted the difference between the two spot models, which might indicate varying spot activity.

In order to understand the evolutionary status of both the components of YY CMi, we made a comparison of their positions with single stars in the $\log\ m$ versus $\log\ L$, $\log\ T$ and $\log\ R$ relations (ZAMS). The primary and secondary components are found to be slightly overluminous and bigger in size when compared to stars of the same mass. This evolution is much less than indicated by the solution of [18, Niarchos et al. (1998)]. In the H-R diagram ($\log\ T_{\rm e}$ versus $\log\ L$, ZAMS) both the components are above but near the ZAMS suggesting that both of them have left the main sequence and have come into contact.

Finally, we point out that our solution is based on photometric data only and hence the conclusions are tentative. It is suggested that spectroscopic observations would give a better understanding of the properties and the evolutionary status of this interesting contact binary.

Acknowledgements

We thank Shri. S. Muneer for his help in preparing the graphs on computer. We also thank the referee, Dr. P.G. Niarchos, for his comments which improved the quality of the paper. MBKS wishes to thank the Council of Scientific and Industrial Research (CSIR), New Delhi for financial assistance through Emeritus Scientists Scheme.