Volume 51 number 1 (2023)
Multi-band photometric observations were acquired for the eclipsing binary stars CD Sex, V365 Sge, V1148 Her, and NSVS 9027851. These binaries have orbital periods less than 0.37 day, stellar surface temperatures less than solar, and total eclipses at primary minimum. New ephemerides were computed using minima timings from the observations, combined with other timings located in the literature. A period analysis found possible long-term orbital period changes for V1148 Her and V365 Sge. In addition, sinusoidal variations in the O–C residuals of V365 Sge indicate a possible low mass circumbinary companion. Photometric solutions using the Wilson-Devinney (WD) program confirmed that each system is a W-subtype contact binary with fill-outs that range from 15 to 22%. The total eclipses provided reliable solution mass ratios for estimating the absolute parameters of the component stars. All the light curves displayed asymmetries with obvious differences in the brightness of Max I and Max II (O’Connell effect). The asymmetries were attributed to magnetic activity and were modeled as hot and cool spots on the stellar surfaces.