BI CVn – A spotted, overcontact, type-W eclipsing binary

• Period behavior is examined, sine fit of Qian et al. (2008) is refuted.
• New RV results, and new VRI and BVRI light curves are presented.
• New WD analyses of our data and also the data of Qian et al. (2008).
• All three models effectively agree within error limits.
• The spot moves from 2005 to 2013. Follow-up observations are suggested.

We present photometric and spectroscopic observations of the eclipsing binary system BI CVn. Wilson–Devinney analysis of its light and radial velocity curves showed that the system is a W-subtype overcontact W-UMa type binary. We computed the absolute physical parameters of the system based on a mass ratio spectroscopically determined in this study. Though the orbital period had changed somehow in the past, it has remained constant for a long time since March 1999, contradicting the previous interpretations suggesting a cyclic variation superimposed on a quadratic change.