Studies of early-type variable stars. XI. Absolute parameters of the Algol system RZ Cassiopeiae.

Abstract

A new spectroscopic orbit is presented for the semi-detached eclipsing binary system RZ Cas (HD 17138, P=1.195 days, alpha(2000.0) = 2 h 48.9 m, alpha = +69 deg 38 min, (A3V+KO), based on Reticon observations with the Dominion Astrophysical Observatory (DAO) 1.2 m telescope and coude spectrograph. We find: m_p sin ³ i = 2.16 +/- 0.07 solar mass, m_s sin³ i = 0.715 +/- 0.02 solar mass (a_p + a_s) sin i = 4.68 +/- 0.07 x 10⁶ km, m_p/m_s = 3.02 +/- 0.07. This is the first direct measure of the mass ratio for this system. The new mass ratio is used to solve the UBV light curves of Chabliss (1976) for the absolute parameters of the system. These in turn are used to apply corrections for non-Keplerian effects to the spectroscopic orbit. Published times of minimum demonstrate that a significant orbital period change occurred during the time interval over which these spectroscopic observations were obtained. This appears to be associated with changes in the spectra observed during this time. We suggest that this is the result of a period of increased mass transfer producing a hot spot or accretion bulge on the surface of the primary component. Stroemgren uvby photometry and low resolution UV (IUE) spectra both suggest a spectral type of A3V for the primary component and a surface composition similar to the Sun. DDO photometry of one primary eclipse of RZ Cas is also presented which appears to show composition anomalies in the secondary component. The absolute parameters of the system are found to be: M_p = 2.205 +/- 0.075 solar mass, m_s = 0.73 +/- 0.02 solar mass, T_p = 8600K +/- 100K, T_s = 4700 +/- 200K R_p = 1.67 +/- 0.03 solar radius, R_s = 1.94 +/- 0.03 solar radius. The system is probably unreddened at a distance of 73 +/- 2pc.