AAVSO: American Association of Variable Star Observers

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

Volume 44 number 1 (2016)

Download this article (pdf)

Pierre de Ponthière
15 Rue Pré Mathy, Lesve, Profondeville 5170, Belgium; pierredeponthiere@gmail.com
Franz-Josef (Josch) Hambsch
12 Oude Bleken, Mol, 2400, Belgium
Kenneth Menzies
318A Potter Road, Framingham, MA 01701
Richard Sabo
2336 Trailcrest Drive, Bozeman, MT 59718


We present the results of a photometry campaign of TU Com performed over a five-year time span. The analysis showed that the possible Blazhko period of 75 days published by the General Catalogue of Variable Stars is not correct. We identified two Blazhko periods of 43.6 and 45.5 days. This finding is based on measurement of 124 light maxima. A spectral analysis of the complete light curve confirmed these two periods. Besides the Blazhko amplitude and phase modulations, another long term periodic phase variation has been identified. This long term periodic variation affects the times of maximum light only and can be attributed to a light-travel time effect due to orbital motion of a binary system. The orbital parameters have been estimated by a nonlinear least-square fit applied to the set of (O-C) values. The Levenberg-Marquart algorithm has been used to perform the nonlinear least-square fit. The tentative orbital parameters include an orbital period of 1676 days, a minimal semi-major axis of 1.55 AU and a small eccentricity of 0.22. The orbital parameter estimation also used 33 (O-C) values obtained from the SWASP survey database. Spectroscopic radial velocity measurements are needed to confirm this binarity. If confirmed, TU Com would be the first Blazhko RR Lyrae star detected in a binary system.