An abnormal radiant luminosity of the contact binary GZ Andromedae and its possible explanation

National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming, Yunnan, China United Laboratory of Optical Astronomy, Chinese Academy of Sciences, China

Corresponding author: Y. Yang, bily@public.km.yn.cn

Received: 24 June 2002
Accepted: 24 September 2002

Abstract

Complete BV light curves of the W UMa type binary GZ And is presented in this paper. From the present times of minimum light and those collected from the references, the changes in the orbital period of the system are analyzed. The result reveals that the orbital period of GZ And continuously increased at a period change rate of . The observed orbital period increase of GZ And may be explained by a mass transfer rate from the smaller to the larger component of The present light curves are analyzed by means of the latest version of the Wilson-Devinney code. The results suggest that GZ And is a W-subtype W UMa contact binary with a mass ratio of 0.511. The present photometric mass ratio is in agreement with that obtained spectroscopically by Lu & Rucinski ([CITE]). Combining the present photometric solution with the spectroscopic orbital elements by Lu & Rucinski ([CITE]), we give absolute dimensions of GZ And. The determined masses and radii of the components show that GZ And is an unevolved main-sequence binary, but the luminosity of the primary is abnormally low for the same mass main-sequence star. The low luminosity of the primary may be explained by transformation between gravitational energy and thermal energy of the system.