SZ Sculptoris: Light Curve Analyses and Period Study of the Totally Eclipsing, Galactic South Pole, Solar-Type Binary

Volume 48 number 2 (2020)

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Ronald G. Samec
Faculty Research Associate, Pisgah Astronomical Research Institute, 1 PARI Drive, Rosman, NC 28772;
Walter Van Hamme
Florida International University, Department of Physics, 11200 SW 8th Street, CP 204 Miami, FL 33199;
Robert Hill
Department of Chemistry and Physics, Bob Jones University 1700 Wade Hampton Boulevard, Greenville, SC 29614;


We report here on the first precision BVRI observations, analysis and period study of SZ Sculptoris (GSC 6990-0597), a solar type (T ~ 5040 K), shallow contact, eclipsing binary. It was observed on 2019 October 05 and 2019 November 05 and 07 in remote mode with the Cerro Tololo InterAmerican Observatory 0.6-m SARA South reflector by R. Samec and R. Hill. The amplitude of the light curves was 0.74, 0.67, 0.65, and 0.61 mag in B, V, R, I, respectively. Six times of minimum light were calculated from three primary eclipses and three secondary eclipses with our present observations. Eight times of low light were also taken from ASAS-SN observations. Two additional timings were taken from the BBSAG Bulletin No. 39 and from APASS observations. From this 41-year interval orbital period study, it was found that the period is decreasing. This may be due to angular momentum loss (AML) resulting from rotating ion streams leaving along stiff magnetic bipolar field lines from the system. A linear ephemeris was also calculated. A BVRI Bessel filtered Wilson-Devinney Program (wd) solution gives a mass ratio, m2 / m1 = 0.3680 ± 0.0007, a small component temperature difference of 160 K, and a contact fill-out of only 7%. Thus, the system is in good thermal contact with a low fill-out. A mid-latitude spot (colatitude of 70°), radius of 18°, and T-factor of 0.66 ± 0.01 was calculated. The system is a W-type W UMa binary. An eclipse duration of ~ 21 minutes was determined for the primary eclipse and the light curve solution.