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IR observations of the dwarf nova U Geminorum show the periodic double wave of an ellipsoidal variable, with an amplitude of 0.25 mag, which is reproduced in calculations of the rotational light curve of the tidally distorted red dwarf star in the system. This star, which is required to fill U Geminorum's Roche lobe, exhibits a variation amplitude which is consistent with (1) the expected geometrical elements of the system, (2) convective gravity darkening, and (3) a moderate degree of limb darkening. Agreement with observations is improved by the reflection effect if only about 1/4 of the observed hot star luminosity is seen by the cool star. The ellipsoidal variation marks the orbital conjunctions for reference with the times of the optical eclipse of the bright spot. The system's IR colors are those of a middle M dwarf star.
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Panek et al. (1982) studied this question.
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