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A Multi-year Multi-passband CCD Photometric Study of the W UMa Binary EQ Tauri

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Kevin B. Alton

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

Received June 5, 2009; revised August 7, 2009; accepted September 1, 2009

Abstract
A revised ephemeris and updated orbital period for EQ Tau have been determined from newly acquired (2007–2009) CCD-derived photometric data. A Roche-type model based on the Wilson-Devinney code produced simultaneous theoretical fits of light curve data in three passbands by invoking cold spots on the primary component. These new model fits, along with similar light curve data for EQ Tau collected during the previous six seasons (2000– 2006), provided a rare opportunity to follow the seasonal appearance of star spots on a W UMa binary system over nine consecutive years. Fixed values for q, Ω, T₁, T₂, and i based upon the mean of eleven separately determined model fits produced for this system are hereafter proposed for future light curve modeling of EQ Tau. With the exception of the 2001 season all other light curves produced since then required a spotted solution to address the flux asymmetry exhibited by this binary system at Max I and Max II. At least one cold spot on the primary appears in seven out of twelve light curves for EQ Tau produced over the last nine years, whereas in six instances two cold spots on the primary star were invoked to improve the model fit. Solutions using a hot spot were less common and involved positioning a single spot on the primary constituent during the 2001–2002, 2002–2003, and 2005–2006 seasons.