AAVSO: American Association of Variable Star Observers

Period Analysis, Photometry, and Astrophysical Modelling of the Contact Eclipsing Binary BC Gruis

Volume 44 number 1 (2016)

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David J. W. Moriarty
School of Mathematics and Physics, The University of Queensland, Qld 4072, Australia; djwmoriarty@bigpond.com


BC Gruis is a W UMa type contact binary system of the W-subtype with the primary minimum 0.1 magnitudes fainter than the secondary minimum. The period is currently 0.3073060 ± 0.0000001 days; it was 4 seconds longer prior to 2000. There were small modulations of 0.001 – 0.003 days in the Observed–Calculated diagram due to asymmetry in the light curves, most likely caused by star spots. An astrophysical model of the system was developed with the mass ratio of 1.16 determined from published spectral data. The best fit to light curves in B, V and I pass bands in 2014-9-30 was given by including 2 large cool star spots on the more massive, cooler component and 1 cool spot on the hotter star. In 2015-9-8, the asymmetry in the light curves was different and was modelled best with a hot spot on the more massive component at the neck joining the stars and 1 cool spot on the other component.