Possible substellar companions in low-mass eclipsing binaries: GU Bootis and YY Geminorum

¹ Astronomical Institute, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
e-mail: wolf@cesnet.cz
² Astronomical Institute, Academy of Sciences, Fričova 298, 251 65 Ondřejov, Czech Republic
³ Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo nám. 13, 746 01 Opava, Czech Republic
⁴ Variable Star and Exoplanet Section of the Czech Astronomical Society, Czech Republic
⁵ Observatory Valašské Meziříčí, Vsetínská 78, 757 01 Valašské Meziříčí, Czech Republic
⁶ Observatory Prostějov, Kolářovy sady 3348, 796 01 Prostějov, Czech Republic
⁷ Faculty of Civil Engineering, University of Technology, Brno, Czech Republic
⁸ Observatory Mladá Boleslav, 294 04 Dolní Bousov, Czech Republic
⁹ Observatory Úpice, U Lipek 160, 542 32 Úpice, Czech Republic

Received: 25 June 2018
Accepted: 22 September 2018

Abstract

We present the next results of our long-term observational project to analyze the variations in the orbital periods of low-mass eclipsing binaries. About 70 new precise mid-eclipse times recorded with a CCD were obtained for two eclipsing binaries with short orbital periods: GU Boo (P = 0.​^d49) and YY Gem (0.​^d81). Observed-minus-calculated diagrams of the stars were analyzed using all reliable timings, and new parameters of the light-time effect were obtained. We derived for the first time or improved the short orbital periods of possible third bodies of 11 and 54 years for these low-mass binaries, respectively. We calculated that the minimum masses of the third components are close to 50 M_Jup, which corresponds to the mass of brown dwarfs. The multiplicity of these systems also plays an important role in the precise determination of their physical parameters.