RW Dor: A G-type shallow contact binary with new orbital period investigation

Abstract

New CCD photometric light curves of short period (P=0.285d) eclipsing binary RW Dor are presented. The observations performed with the PROMPT-8 robotic telescope at CTIO in Chile from March 2015 to March 2017. The other eclipse timings were obtained from the 2.15-m JS telescope at CASLEO, San Juan, Argentina in December 2011. By light-curve analysis, it is found that RW Dor is a W-type shallow contact binary with a fill-out factor f ∼ 11% and high mass ratio q ∼ 1.587 (1/q = 0.63), where the hotter component is the less massive one (M 1 ∼ 0.52M ⊙ and M 2 ∼ 0.82M ⊙ ). For orbital period investigation, the new fifteen eclipse times and those in previous published were compiled. Based on O − C analysis with very weak evidence suggests that a longterm period decrease with a rate of dP/dt = −9.61 × 10 −9 d yr −1 is superimposed on a cyclic variation (A 3 = 0.0054 days and P 3 = 49.9 yrs). The long-term period decrease can be interpreted as mass transfer from the more massive component to the less massive one or combine with the angular momentum loss (AML) via magnetic braking. In addition, with the marginal contact phase, high mass ratio (1/q > 0.4) and the long-term period decrease, all suggest that RW Dor is a newly formed contact binary via a Case A mass transfer and it will evolve into a deeper normal contact binary. If the cyclic change is correct, the light-travel time effect via the presence of a cool third body will be more plausible to explain for this.