THE AGE-MASS RELATION FOR CHROMOSPHERICALLY ACTIVE BINARIES .1. THE EVOLUTIONARY STATUS

In this paper we present a study of the evolutionary status of a sampl e of chromospherically active binary systems for which accurate determ inations of their stellar parameters are available. Stellar ages have been obtained by using evolutionary tracks. The agreement between the estimates of ages for the two components of a given system is very goo d, which proves the reliability of our method. It has been possible to separate the chromospherically active binaries in three groups, accor ding to the mass of the primary component: evolved stars with masses i n the range 2.5-5 M(circle dot) , evolved stars (subgiants) with M sim ilar or equal to 1.4 M(circle dot) and main-sequence stars with M simi lar or equal to 1.1 M(circle dot) . We have found a relationship betwe en stellar masses and ages of the form Log Age = 9.883(+/-0.022) - 2.9 65(+/-0.122) Log (Mass/M(circle dot)). This relationship is very close to that for stars on the TAMS. The relation can be understood, in the framework of the evolution of the components and orbital elements of binary systems, as an effect of the increase of the stellar radius as the components evolve off the main sequence, and the decrease of the r otation period due to tidal effects which leads to enhanced chromosphe ric emission levels, several times higher than that of the Sun. The re lationship has a dependence on rotation, due to the fact that for a gi ven range of masses, younger stars rotate faster. We have also found t hat the more evolved stars are the more active, for a given interval o f rotation periods.