Period Changes of W UMa Type Contact Binary SS ARIETIS

Abstract

The BVR CCD photometric observations of W UMa-type eclipsing binary 55 Ari were made on ten nights from November 1996 to December 1996. Eight new times of minimum lights were derived. The analysis of times of minima of 55 Ari confirms the suggestions of other previous investigators that the orbital period of 55 Ari have been suffering from a sinusoidal variation. The amplitude and period for the cyclic period changes were calculated as about 58y and 0.dO53, respectively. The period variation has been discussed in terms of two potential mechanisms: 1) the light-time effect due to a hypothetical third body arid 2) deformations in the convective envelope of a magnetically active component. In the earlier case, the third body has a mass of 1.3Msolar if exists, in the form of a white dwarf or a binary system. It seems that the system velocities from the spectroscopic observations supports this interpretation. Meanwhile in the latter case, the primary component is mainly responsible for the magnetic activity of this system with a theoretical magnitude amplitude of ¡¾0.m08. However, we cannot make a conclusion which is reasonable explanation at this point, due to lack of observational data. Moreover, the period variation of 55 Ari shows duplication about 14y cyclic period with an amplitude of about 0.d001 to the above periodic change. We also cannot make an acceptable conclusion for it at this time.