Deep, low mass ratio overcontact binary systems. XIII. DZ piscium with intrinsic light variability

摘要

New multi-color photometry for the eclipsing binary DZ Psc was performed in 2011 and 2012 using the 85 cm telescope at the Xinglong Station of the National Astronomical Observatories of China. Using the updated Wilson-Devinney (W-D) code, we deduced two sets of photometric solutions. The overcontact degree is f = 89.7(±1.0), identifying DZ Psc as a deep, low mass ratio overcontact binary. The asymmetric light curves (i.e., #1LC2 in 2012) were modeled by a hot spot on the primary star. Based on all of the available light minimum times, we discovered that the orbital period of DZ Psc may be undergoing a secular period increase with a cyclic variation. The modulated period and semi-amplitude of this oscillation are Pmod = 11.89(±0.19)yr and A = 0.0064(±0.0006) days, which may be possibly attributed to either cyclic magnetic activity or light-time effect due to the third body. The long-term period increases at a rate of dP/dt = +7.43(±0.17) × 10-7 days yr-1, which may be interpreted as conserved mass transfer from the less massive component to the more massive one. With mass transferring, DZ Psc will finally merge into a rapid-rotation single star when J_(spin)/J_(orb) > 1/3.