The massive system V375 Cassiopeia is a semidetached mass-transfer binary with a massive stellar companion

Abstract

ABSTRACT V375 Cassiopeia (V375 Cas) is an early B-type close binary with an orbital period of 1.4734273 d. Based on high-quality and continuous light curves from the Transiting Exoplanet Survey Satellite (TESS) and new low-resolution spectra, we have determined photometric solutions of the eclipsing binary using the Wilson–Devinney method. We have found that V375 Cas is a semidetached binary where the secondary component fills the critical Roche lobe. Meanwhile, its O − C diagram was constructed with the data spanning 122 yr. An upward parabolic variation is discovered to be superimposed on a cyclic modulation with a semi-amplitude of 0.0938 (±0.0143) d and a period of 118.74 (±12.87) yr. The parabolic change reveals a period increase at a rate of ${\rm d}p/{\rm d}t = +5.42 \times {10^{-7}}\, {\rm d} \,\mathrm{yr}^{-1}$. Both the semidetached configuration and the period increase suggest that V375 Cas is undergoing a late case A mass transfer from the less-massive component to the more-massive component. The cyclic change is attributed to be the effect of the light travel time via the presence of a third body. The minimum mass of the tertiary companion is estimated as M3 = 4.24 (±0.87) M⊙, which orbits around the central eclipsing binary with a nearly circular orbit (e = 0.184). It is detected that the light contribution of the third body is about 8.0 per cent, indicating that it is a massive main-sequence star. All the results reveal that V375 Cas is a hierarchical triple system where a massive main-sequence star accompanies a massive semidetached mass-transfer binary at an orbital separation of 60.3 au.