A photometric study of the W UMa-type system U Pegasi

¹ Astronomical Observatory, Volgina 7, 11050 Belgrade, Yugoslavia
² Section of Astrophysics-Astronomy & Mechanics, Dept. of Physics, Athens University, GR Zografos 157 84, Athens, Greece e-mail: elivan@atlas.uoa.gr
³ Astron. Institute, National Observatory of Athens, PO Box 20048, 118 10 Athens, Greece

Corresponding author: G. Djurašević, gdjurasevic@aob.bg.ac.yu

Received: 14 April 2000
Accepted: 20 November 2000

Abstract

In the present study, the activity of the eclipsing binary of the W UMa-type system U Peg is examined by analysing the photoelectric observations covering the period from 1950 to 1989. During this period, the light curves show significant differences and asymmetries. The analysis of the corresponding light curves is made using Djurašević's inverse problem method. To explain the light-curve asymmetries and variations, we used a Roche model that involved regions containing spots on the components. The analysis shows that the system U Peg is in an overcontact configuration (). The Roche model with spotted areas on the cooler component yields a good fit of the observations for the whole set of the analysed 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 evolution and motion of spotted areas on the cooler component. According to the obtained results, the spotted areas cover a significant part of the stellar surface; the changes in their location and size with time are examined.