A light synthesis study of W Ursae Majoris

Abstract

A common set of Roche model parameters produces an accurate fit to I, V, and B data for W Ursae Majoris. The R data are defective. Two pairs of cool photospheric starspots are adopted in producing the fit. The model also adopts the cross-correlation radial velocity obtained by McLean and satisfactorily eliminates evidence, cited in the literature, for a third body in the system. Changing starspot longitudes, while maintaining fixed angular diameter, latitude, and temperature contrast from the adjacent photosphere, can simulate all of the types of light curve instability recorded in historical W Ursae Majoris light curves. Although the theoretical curve accurately fits primary minimum in U, the theoretical curve is too shallow at secondary minimum. A hot secondary explanation of W-type light curves, rather than starspots on an otherwise barotropic photosphere is argued.