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ejaavso412227

eJAAVSO  

Simultaneous CCD Photometry of Two Eclipsing Binary Stars in Pegasus—Part 2: BX Peg

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Kevin B. Alton

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

Received December 5, 2012; revised January 3, 2013; accepted January 3, 2013

Abstract

BX Peg is an overcontact W UMa binary system (P = 0.280416 d) which has been rather well studied, but not fully understood due to complex changes in eclipse timings and light curve variations attributed to star spots. Photometric data collected in three bandpasses (B, V, and Ic) produced nineteen new times of minimum for BX Peg. These were used to update the linear ephemeris and further analyze potential changes in orbital periodicity by examining long–term changes in eclipse timings. In addition, synthetic fitting of light curves by Roche modeling was accomplished with the assistance of three different programs, two of which employ the Wilson–Devinney code. Different spotted solutions were necessary to achieve the best Roche model fits for BX Peg light curves collected in 2008 and 2011. Overall, the long–term decrease (9.66 × 10–3 sec y–1) in orbital period defined by the parabolic fit of eclipse timing data could arise from mass transfer or angular momentum loss. The remaining residuals from observed minus predicted eclipse timings for BX Peg exhibit complex but non–random behavior. These may be related to magnetic activity cycles and/or the presence of an unseen mass influencing the times of minimum, however, additional minima need to be collected over a much longer timescale to resolve the nature of these complex changes.

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