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

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Kevin B. Alton

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


Received June 8, 2009; revised October 8, 2009; accepted October 8, 2009

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.

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