A PERIOD STUDY OF XZ ANDROMEDAE

A period study of an evolved Algol system XZ And has been attempted by using additional new data. The (O-C) diagram formed by the times of m inimum light and thus orbital period of the system was found explainab le in terms of the beat effect of two (or possibly three) cyclic varia tions differing in periods (P-1=137.5 yr, P-2=36.8 yr, and P-3=11.2 yr ) and amplitudes. We examined three possible explanatory mechanisms (a psidal motion of the slightly elliptical orbit, light time effect due to additional objects in the system, and the period modulation due to magnetic activity cycle of cool secondary component star). The observa tional evidences reject the possibility of apsidal motion effect on th e period variation. One of the cyclic effects (probably with the short est period P-3=11.2 yr) may be related with the cyclic magnetic activi ty of the secondary component. The third body hypothesis requires one or two under-luminous stars (with total mass of about 3 M.) around the system.