2020JAVSO..48..124S

CCD Bessell BVRI light curves of TYC 9291-1051-1 were taken on 9, 20, and 28 August 2019 in remote mode at Cerro Tololo InterAmerican Observatory with the 0.6-m SARA South reflector by R. Samec and W. Van Hamme. The variability of TYC 9291-1051-1 (UNSW V-633) was discovered by the University of New South Wales Extrasolar Planet Search (Christiansen et al. 2008), which classified it as an EW variable with a magnitude of V = 10.90 and a period of 0.42713 d. Five times of minimum light were determined from our present observations, which include two primary eclipses and three secondary eclipses. Linear and quadratic ephemerides were determined from all available times of minimum light. A ∼ 13.3-year period study (∼ 11,400 orbits) reveals that the period is increasing. This could be due to mass transfer making the mass ratio more extreme. Wilson-Devinney analyses reveals that the system is a A-type W UMa binary (P-shift = 0.5) with a mass ratio that is somewhat extreme, M2/ M1 = 0.260 ± 0.004 (star 1 is the more massive component, M1/ M2 = 3.8). The total eclipse makes this a good determination (Terrell and Wilson 2005). Its Roche lobe fill-out is ∼ 32%. The solution has two major spot regions, a mid-latitude cool spot of radius 19 ± 5 degrees and an equatorial weak hot spot (T-factor = 1.06) of 21 ± 6 degrees. We note that the hot spot is on the on the gainer which covers the Lagrangian, L1, point. This probably has to do with the mass transfer. The spot regions were variable during the 19-day interval of observation. The temperature difference of the components is about ∼ 270 K, with the more massive component as the hotter one, so it is an A-type W UMa binary. The inclination is 83.25 ± 0.50 deg. The primary (with P-shift 0.5) minimum has a time of constant light with an eclipse duration of 13.3 minutes.