2004A&A...420.1039A

In the present study, the activity of the eclipsing binary of the W UMa-type system SW Lac is examined by analysing the new BV photoelectric observations obtained in 2001, 2002 and 2003 at the Ankara University Observatory. During this period, the seasonal light curves show significant differences and asymmetries. A simultaneous analysis of the light curves is made using Djurasevic's inverse-problem method. To explain the light-curve asymmetries and the different maximum light levels in the seasonal light curves we used a Roche model that involved regions containing spots on the components. The analysis shows that SW Lac is in an overcontact configuration with a relatively high degree of overcontact f_over ∼ 31%. The Roche model with spotted areas on the more massive and cooler component yields a good fit of the observations for the whole set of the seasonal light curves, without any changes of the basic system parameters. This indicates that the complex nature of the light-curve variations during the examined period can be explained by the changes of spotted areas on the cooler component, which cover a significant part of the stellar surface.