MAGNETIC ACTIVITY AND EVOLUTION OF ALGOL-TYPE STARS

We examine the possibility of tracing dynamo action in mass-losing sta rs that are components of Algol-type binaries. Our analysis is based o n the calculation of the non-conservative evolution of a system that i nitially consists of a 1.65-M. star with a small helium core and a 0.9 9-M. main-sequence companion. We perform our calculations for the evol utionary model of S Cnc in which a more massive companion fills its Ro che lobe at the orbital period of the system P(orb)similar to 1.12 d. We show that to maintain the late stages of evolution of this system, which are driven by stellar 'magnetic braking', an efficient mechanism that produces large-scale surface magnetic fields in a donor star is needed. We discuss the relevance of dynamo action in a donor star to t he stages of accelerated mass transfer in the evolution of Algol-type systems.