Absolute parameters for binary systems

II. The late-type system ZZ Ursae Majoris

¹ Departamento de Astronomía y Astrofísica, Universidad de Valencia, Dr. Moliner 50, E-46100, Burjassot, Valencia, Spain
² Departamento de Física Aplicada, E.U.I.T. Industrial, Universidad Politécnica de Madrid, Ronda de Valencia 3, E-28012 Madrid, Spain

Send offprint request to: R. Clement

Received: 20 December 1996
Accepted: 27 January 1997

Abstract

New light curves of the late-type binary system ZZ UMa were obtained during a uvby and Hβ monitoring program on low mass eclipsing binaries, that has been carried out in a six year photometric observational program (Clement et al. 1997a, Paper I). The main goal of the program is to obtain accurate absolute parameters for stars in the low and intermediate mass range, in order to improve the Mass-Luminosity Relationship (MLR) at the end of the main sequence. This paper presents a complete analysis of the first light curves of the late-type detached eclipsing binary ZZ UMa. This binary system has been observed during eight campaigns at the Calar Alto Observatory (Almeria, Spain). The activity wave superposed on the eclipse light curve has been estimated, by using a new iterative fitting method (Clement et al. 1997b, Paper II). The interpretation of the wave suggests the existence of two active zones of similar intensity, separated by areas at higher temperature. Once the activity wave was subtracted from the light curves, we adjusted the geometrical solution using the EBOP code. Radiative parameters for both stars have been derived from the light curves. Combining the masses deduced from the radial velocity curves (Popper 1995), with the calculated geometrical and radiative values, we computed the absolute parameters for both components. We can conclude that the system is composed of two main sequence G-type stars with masses, radii and chemical composition similar to the Sun.