Orbital Period Studies of Three Algols: TW And, RW Leo, and AY Vul

Abstract The changes in the orbital periods of three EA-type eclipsing binaries, TW And, RW Leo, and AY Vul, are discussed based on an analysis of their $O-C$ curves. For RW Leo, its orbital period was revised and, assuming a cyclic oscillation in the orbital period, a period of 38.4 yr was determined. For the other two systems, TW And and AY Vul, their $O-C$ diagrams show complex variations. Under the assumption of periodic oscillation, cyclic changes with periods of 56.4 and 78.6 yr were discovered to superimpose on upward parabolic changes, indicating a secular period increase. The secular period increases for the two binary systems indicate that they are on an active phase of mass transfer. Assuming the oscillations in the periods to be caused by light-time effects due to the presence of “third bodies” rotating around these binary stars, the orbital parameters of the third bodies were determined. For RW Leo, it is possible to detect an additional third body photometrically and spectroscopically. However, for the other two systems, TW And and AY Vul, it is less likely to see additional bodies, unless the orbital inclination is very small (i.e., $i^{\prime}<30^{\circ}$). New photometric and spectroscopic observations and a careful analysis of those data are needed to check the presence of third bodies.