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Session 45 - Eclipsing Binaries.
Display session, Thursday, January 08
Among the longer-period, double-lined spectroscopic binary systems known to be eclipsing are many that have no modern photometric analysis. Several of these systems are being studied at Southwest Missouri State University as part of a long term study of binary stars. One of these stars, V448 Cygni, was discovered to be variable in 1939 and is a semi-detached Beta-Lyrae type binary. The first light curve was obtained in 1942 by J. Ashbrook based on his visual measurements. The system appears to consists of a supergiant and a main sequence star. The binary is also a member of the open cluster NGC 6871. One of the difficulties in obtaining accurate masses for this system has been the lack of modern photometry and radial velocity measurements. In 1996, Harries et al. published modern spectroscopic data and used the 1942 light curve of Ashbrook to perform their light curve analysis. They assumed a temperature for the main sequence star of 30,000 K and found the supergiant to be near 20,460 K. They obtained a mass ratio of 1.8022 with the main sequence and supergiant stars having masses of 14.0 and 25.2 solar masses, respectively, at an inclination of 83.2 degrees. In addition, it has been shown that the system exhibits a gaseous cloud interacting among the two stars. This complicates the light curve and causes the minimum to change depths, particularly the secondary.
We present new BVRI photometry obtained at the SMSU Baker Observatory 0.4-meter with a Photometrics PM512 CCD. Preliminary light curve analysis using the Wilson-Devinney code gives an inclination closer to 77.5 degrees, resulting in masses around 14.6 for the main sequence star and 26.4 for the supergiant. These masses are slightly higher than those published by Harries et al. We also assumed a temperature of 30,000 K for the main sequence star and a mass ratio of 1.8022. We found the temperature of the supergiant to be near 22,000 K. We have also found in necessary to place a hot spot on the supergiant to model the anomalies in the observed light curve. This research is supported by NSF Grant # AST-9315061 and NASA Grant # NGT-40029.
Program listing for Thursday