The secondary minimum in YY Herculis: Evidence for a tidally distorted giant

We present and analyze quiescent UBVRI light curves of the classical symbiotic binary YY Her. We show that the secondary minimum, which is clearly visible only in the quiescent VRI light curves, is due to ellipsoidal variability of the red giant component. Our simple light curve analysis, by fitting of the Fourier cosine series, resulted in a self-consistent phenomenological model of YY Her, in which the periodic changes can be described by a combination of the ellipsoidal changes and a sinusoidal changes of the nebular continuum and line emission.