The Case for Third Bodies as the Cause of Period Changes in Selected Algol Systems

Many eclipsing binary star systems show long-term variations in their orbital periods, evident in their O-C (observed minus calculated period) diagrams. With data from the Robotic Optical Transient Search Experiment (ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1 m data, and recent American Association of Variable Star Observers (AAVSO) data, we revisit Borkovits and Hegedüs's best-case candidates for third-body effects in eclipsing binaries: AB And, TV Cas, XX Cep, and AK Her. We also examine the possibility of a third body orbiting Y Cam. Our new data support their suggestion that a third body is present in all systems except AK Her, as is revealed by the sinusoidal variations of the O-C residuals. Our new data suggest that a third body alone cannot explain the variations seen in the O-C residuals of AK Her. We also provide a table of 143 eclipsing binary systems that have historical AAVSO O-C data with new values computed from the SkyDOT database.