A Unified Roche-Model Light Curve Solution for the W UMa Binary AC Bootis

Volume 38 number 1 (2010)

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Kevin B. Alton

UnderOak Observatory, 70 Summit Avenue, Cedar Knolls, NJ 07927

Abstract

Over forty years of photoelectric light curves published by five different investigators and CCD data more recently (2006) collected in V- and R-bands were analyzed using a Roche-type geometry as implemented by the Wilson-Devinney code. This has not only resulted in a revised ephemeris and orbital period for AC Boo, but has lead to a unified light curve solution. Based upon moments of minima residual analysis, AC Boo has experienced a continual increase in orbital period for the past forty-eight years or longer, thereby suggesting an ongoing exchange of mass. Fourier analysis also revealed possible periodicity in O-C residuals which is heavily influenced by a putative sinusoidal-like wave most apparent over the past twenty years. The weight of evidence, nonetheless, points to a W-subtype W UMa system that does not necessarily vary as the result of an unseen companion (third light) but rather by spot formation on either stellar component. A series of spotted solutions, based upon a nearly symmetrical light curve collected in 1962, has provided a theoretical fit of all published photoelectric data that largely accounts for the observed peak asymmetry, unequal successive maxima, and varying depths of minima.