TESS light curves and period changes in low-mass eclipsing binary BB Persei

Abstract

We present a detailed analysis of the low-mass detached eclipsing binary system BB Persei, which contains two K-type stars in a circular orbit with a short period of 0.4856 d. We used light curves from the Transiting Exoplanet Survey Satellite (TESS), which observed BB Per in five sectors, to determine its photometric properties and a precise orbital ephemeris. The solution of the TESS light curve in PHOEBE results in a detached configuration, where the temperature of the primary component was fixed to T1=5300 K according to LAMOST, which gives us T2=5050±50 K for the secondary. The spectral type of the primary component was derived as K0 and the photometric mass ratio was estimated q=0.90. Slow period changes on the current O-C diagram spanning the past 25 years indicate the presence of a third body orbiting the eclipsing pair with an orbital period of about 22 years. The companion could be a red dwarf of spectral type M6–M7 with a minimal mass of about 0.1 M⊙. The characteristics and temporal variation of the dark region on the surface of the secondary component were estimated.