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GT Ursae Majoris AB - a Possible Quadruple System

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Dimitrov W. , Tomov T. , Kamiński K. , Polińska M. , Iliev I. , Kamińska M. K.

tom Vol. 68, No. 2

141--158

We present the first spectroscopic study of an eclipsing system GT UMa. Our spectra show that the main visual component A is a triple-lined star, which consists of a close eclipsing pair and a farther third component. Radial velocity measurements show evidence of reflex motion. We used Hipparcos and our own R-band light curves for the analysis. These results enabled us to calculate absolute parameters of the eclipsing binary system: 1.37 M⊙ and 1.31 M⊙ and corresponding radii 2.11 R⊙ and 1.63 R⊙. Both eclipsing components are evolved. The orbital period of the eclipsing subsystem is 1.2 d and the semi-major axis - 6.5 R⊙. The wide orbit has low radial velocity amplitude and its parameters are difficult to determine. We obtained a preliminary solution which must be confirmed with future observations. The preliminary period of the wide orbit is 394 d and the lower limit for the semi-major axis - 174 R⊙ (0.81 a.u.). We estimated the mass of the third body to about 1.1 M⊙. Additionally, we investigated the visual companion B. We obtained spectra of this star and measured the radial velocity which is very close to the one of the component A. The proper motions and the parallax are also similar. These are strong arguments that component B is gravitationally bound with the main triple system A.