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Session 77 - Binary Stars.
Display session, Wednesday, January 15
Metropolitan Ballroom,

[77.14] RZ Cassiopeiae: Evidence for Spots on the Surface of the Primary Star in an Algol-type Eclipsing Binary System

S. M. Davis, T. J. Balonek (Colgate Univ.)

The bright Algol-type eclipsing binary system RZ Cassiopeiae is known to exhibit irregular period changes as well as changes in the shape of the primary minimum light curve. Deviations from a simple partial eclipse light curve have been reported by other investigators in some, though not all, eclipses. We report CCD observations of five primary minima in 1996 obtained with the Colgate University Foggy Bottom Observatory 16-inch telescope. From these observations we construct an average "template" light curve in V for the primary eclipse and show that individual eclipses may differ significantly in shape from this template. Consecutive minima often have distinctly different shapes. The residuals between an individual light curve and the template show quasi-periodic oscillations with a "period" of about 25 minutes (corresponding to 0.013 in phase) and amplitude +/- 0.04 magnitude. The residuals of consectutive minima appear similar in structure, though displaced in time by about 15 minutes from each other. We interpret the oscillations in the light curves as evidence for hot and cool spots on the surface of the main sequence primary star resulting from mass exchange from the cooler subgiant secondary. The changes in the light curve shape indicate a non-synchronous rotation of the primary star.

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