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Description
The eclipsing binary RS Canum Venaticorum (RS CVn) was first discovered in 1914. Fifty-five years and more than ten investigations later, this system is not yet fully understood. The source of the confusion in the dynamical and physical properties has been distortions in the light curve. This paper presents the first extensive three color photoelectric observations of the system and suggests that the fundamental properties are even less certain than has been thought. The first model based on adequate observational evidence is also presented. The binary components are thought to be of spectral types F4IV-V and KOIV. The orbital period is approximately 4~7978, but may vary by nearly 0.01 of this amount. There has been some debate as to whether the variation is sinusoidal (with a period on the order of thirty-five years) or semiregular. The masses (in solar units) determined from the rather extensive spectroscopy of Joy (1930) are 1.85 for the hotter star and 1.71 for the cooler star. But the results of Popper in the late 1950s indicates masses of 1.34 and 1.40 for the hot and cool components, respectively. The source of the 22 percent difference is a dichotomy of 13 km/sec in the K values of the two authors. The center of mass velocities differ by 6 km/sec. Photoelectric investigations have failed to cover more than one color, with the exception of the altogether inadequate results of Popper. This thesis reports the first extensive three color photo- electric observations of the system. These observations were made at the San Diego State College Observatory in the years 1962-63 and 1965-67. Previously unnoted changes in the light curve are reported. These include short term but large scale changes in the depth of primary eclipse (up to 0~2 in ultraviolet in a few weeks). Lesser but related changes occur in secondary eclipse and the maxima. The depressed region of the light curve is found to "slip backward" in phase coordinate with time. The principal results of this investigation are: 1. To reveal that the large scale distortion of the maxima and eclipses is linked directly with the KO star and is most probably due to pulsation of that star. The mean period of pulsation is found to vary from between eight to twenty-five minutes longer than the orbital period over the years 1963-67. 2. To reject the 1965 hypothesis of Chisari and Lacona that the distortions are caused by a gas cloud with an independent orbital period. Photoelectric observations show that the color behavior of the distortions requires such a cloud to be composed of negative hydrogen ion (a gas not known to exist outside of middle to late type stellar atmospheres). 3. To indicate that the presently accepted mass values are highly suspect because of the pulsating KO star. Evidence is found favoring distortion of the radial velocity curves of Joy and Popper. 4. As the KO star lies well outside the regions of the H-R plane normally occupied by variable stars, it is suggested that the star is undergoing induced oscillations. The coincidence of the orbital and pulsation periods is a supportive argument. Photoelectric evidence is found that may be interpreted to indicate the maximum radius comes after the minimum light output by the pulsator. This is in contradistinction to the light curve-radius relation found from Cepheids and other regular pulsators. Further work is recommended with the justification that new information may be obtained about stars undergoing induced radial oscillations.
