WW GEMINORUM: AN EARLY B-TYPE ECLIPSING BINARY EVOLVING INTO THE CONTACT PHASE

Abstract

WW Gem is a B-type eclipsing binary with a period of 1.2378 days. The CCD photometry of this binary was performed in 2013 December using the 85 cm telescope at the Xinglong Stations of the National Astronomical Observatories of China. Using the updated W-D program, the photometric model was deduced from the VRI light curves. The results imply that WW Gem is a near-contact eclipsing binary whose primary component almost fills its Roche lobe. The photometric mass ratio is qph = 0.48(±0.05). All collected times of minimum light, including two newones,wereusedfortheperiodstudies.TheorbitalperiodchangesofWWGemcouldbedescribedbyanupward parabola, possibly overlaid by a light-time orbit with a period of Pmod = 7.41(±0.04)yr and a semi-amplitude of A = 0.0079 days(±0.0005 days), respectively. This kind of cyclic oscillation may be attributed to the light-travel time effect via the third body. The long-term period increases at a rate of dP/dt = +3.47(±0.04) ×10 −8 dayyr −1 , which may be explained by the conserved mass transfer from the less massive component to the more massive one. With mass transfer, the massive binary WW Gem may be evolving into a contact binary.