Synchronous Rotation in the Eclipsing Binary 68 Herculis Inferred from Doppler Shifts in its Spectrum and Light Curve Modeling
The Journal of the Iowa Academy of Science
Science Hall, Room 123, Loras College, Dubuque, Iowa Our differential photometry of the eclipsing binary 68 Herculis through V-and R-filters shows periodic minima consistent with a previously established period. As a function of its orbital motion, we report spectra over a limited wavelength range encompassing H-alpha 656.3 nm and helium 667.8 nm lines. Doppler shifts of both stars were resolved in H-alpha, while only the more massive star rendered the helium line with Doppler shifts that agree
... r shifts that agree with the radial velocity we derive for it from the H-alpha profile. Sinusoidal curve-fits to the orbital dependence of the radial velocities imply circular orbits for both components, with amplitudes indicating a mass ratio for the two stars in agreement with published values. A subtle Doppler shift associated with stellar rotation is evident in the radial velocity of the primary component as its eclipse commences; modeling indicates this rotation is synchronous with the orbital revolution, an expected tidal effect of near-contact binary systems. INDEX DESCRIPTORS: eclipsing binary, light curve, orbital parameters, Doppler shifts.