Ground-based photometry of the contact binary V1128 Tauri

Ege University Observatory, 35100 Bornova-Izmir, Turkey e-mail: [sevren,cakirli,ibanoglu]@astronomy.sci.ege.edu.tr

Corresponding author: G. Taş, tas@astronomy.sci.ege.edu.tr

Received: 21 January 2003
Accepted: 22 May 2003

Abstract

V1128 Tau is a short period W UMa type eclipsing binary which has a visual companion with a separation of 14″ and a difference in brightness of about 1 mag. We observed the system in B and V filters during two observing seasons using three different telescopes and detectors. We obtained a total of 6063 observational points in each colour. The light curve reveals that V1128 Tau has a totality in the primary eclipse, which lasts about 16 min. The shape of the light curve indicates that V1128 Tauri is a W-type W UMa binary. We subtracted the visual component's light contribution to the total light of the system. We used the latest version of the Wilson-Devinney code for the analysis of the light curves and determined for the first time the geometric and physical parameters of the system. We found that the system consists of late G and early K type components. The more massive, larger component is cooler by about 300 K than its companion. The system has a circular orbit with an inclination of 85°. The light curves show a typical O'Connell effect, maximum I being brighter than maximum II. This difference may arise from a cool or hot region on either component and/or an accretion process between the components. Since the components appear to be later than G2, we assumed a cool spot or group of spots on the cooler component. Therefore, the light curves were also analyzed using the spot hypothesis and the results were compared with those obtained with the no-spot model.