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We present the results of a photometry campaign of TU Com performed over afive-year time span. The analysis showed that the possible Blazhko period of 75days published by the General Catalogue of Variable Stars is not correct. Weidentified two Blazhko periods of 43.6 and 45.5 days. This finding is based onmeasurement of 124 light maxima. A spectral analysis of the complete lightcurve confirmed these two periods. Besides the Blazhko amplitude and phasemodulations, another long term periodic phase variation has been identified.This long term periodic variation affects the times of maximum light only andcan be attributed to a light-travel time effect due to orbital motion of abinary system. The orbital parameters have been estimated by a nonlinearleast-square fit applied to the set of (O-C) values. The Levenberg-Marquartalgorithm has been used to perform the nonlinear least-square fit. Thetentative orbital parameters include an orbital period of 1676 days, a minimalsemi-major axis of 1.55 AU and a small eccentricity of 0.22. The orbitalparameter estimation also used 33 (O-C) values obtained from the SWASP surveydatabase. Spectroscopic radial velocity measurements are needed to confirm thisbinarity. If confirmed, TU Com would be the first Blazhko RR Lyrae stardetected in a binary system.

TU Comae Berenices : Blazhko RR Lyrae Star in a Potential Binary System