Speaker: John J. Zanazzi, University of Toronto, Canadian Institute for Theoretical Astrophysics

Title: Orbital Circularization of Binaries with Resonance Locking from Stellar Evolution

Abstract: Although tidal dissipation in binary stars has been studied for over a century, many theoretical predictions do not match the observed properties of binary population orbits and rotation rates. Both equilibrium and dynamical tidal theories predict different eccentricities at the orbital periods and ages binaries are observed in populations, and many asynchronously rotating binaries have ages longer than their calculated synchronization times. Motivated by these difficulties, we investigate the orbital and rotational evolution of binaries driven by resonance locking, a theory which argues most tidal dissipation occurs from resonances between the host’s natural oscillation frequency (from gravity modes) and the perturber’s tidal potential oscillation frequency, locked by the entropy-profile evolution of the host star. We find orbital evolution via resonance locking to efficiently circularize binaries out to 4-6 days during the pre-main-sequence, and decrease the eccentricities of moderately and highly eccentric binaries out to 100 days. Binary evolution via resonance locking predicts the binary’s synchronization time to be usually longer than the circularization time. Resonance locking can potentially explain the eccentricity distribution of eccentric binaries out to 100 days, but cannot explain the over-abundance of nearly-circular binaries out to 10 days.