SX Piscium: A near-contact mass-transferring binary with a possible brown dwarf companion

Abstract

SX Psc is a short-period Algol-type eclipsing binary whose photometric analysis has long been ignored. Our photometric monitoring of this target covered from 2001 December to 2018 November. Aside from some curves observed at the primary eclipses, the complete four-color light curves in the BVRcIc band were also obtained. Photometric solutions were determined based on the Wilson-Devinney method. It is found that SX Psc is a semidetached binary where the inner Roche lobe of the secondary component has been filled. The filling factor for the primary is about 85% along with an inclination of , indicating that it is a near-contact total eclipsing binary system. Meanwhile, analysis of the O - C curve revealed that the orbital period is increasing continuously at a rate of dP/dt = 4.64(4) x 10(-8)dyr(-1). This is due to the mass transfers from the secondary to the primary component, which is in accord with the semidetached configuration of this binary star. With the assumption of conservative evolution, the mass transfer rate is estimated as 1.96 x 10(-8) M-circle dot yr(-1). By deducting the long-term increasing trend in the O - C diagram, the high-precision data exhibits a cyclic variation, whereas it might be caused by the Applegate mechanism. Moreover, according to the light travel-time effect, there should be a candidate brown dwarf with a mass of no less than orbiting the eclipsing binary. This is perhaps a unique case for an Algol-type binary accompanied by a substellar object.