Schedule Oct 28, 2011
Tidal Asteroseismology
Josh Burkart (UC Berkeley)

The recently discovered Kepler system KOI-54 is a face-on eccentric binary consisting of two similar A stars. Its lightcurve exhibits ~20 tidally excited pulsations at perfect harmonics of the orbital frequency, and another ~10 nonharmonic pulsations. Analysis of such data is a new form of asteroseismology in which oscillation amplitudes and phases rather than frequencies contain information that can be mined to constrain stellar properties. I will discuss the physics of mode excitation and the range of harmonics expected to be observed. I will then show the results of numerical modeling of the pulsation spectrum, using a nonadiabatic stellar oscillation code including rotation in the "traditional approximation", which qualitatively reproduce the observations. I will discuss the evolutionary history of the KOI-54 system, and will show that the system is likely in a state of stochastic dynamical pseudosynchronization with stellar spin periods of ~1.5 days, significantly faster than the classical theoretical prediction of ~2.5 days. Time permitting, I will also address the nonharmonic pulsations observed in KOI-54, and show that they can be produced by nonlinear three-mode coupling.

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