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The studies of binary stars must address the complexities such as mass transfer and tides. I will demonstrate the effects of mass transfer, tides, and nonlinearity on stellar oscillations. 1) In the so-called EL CVn binaries, the mass-transfer leads to rejuvenation of the mass gainer and can produce high frequency Scuti stars and Slowly Pulsating B stars. The accretion of material can change the mode excitation as well as mode frequencies. 2) In some binaries with elliptical orbit (Heartbeat stars), tidal force can directly induce stellar g modes. The amplitudes and phases of these modes can be modelled with linear theory; 3) Some of the modes can also be weakly nonlinear and further produce daughter modes visa parametric instability. The mode behaviour of coupled systems can be rich and complicated, including period doubling, intermittency and various ways to chaos.
In the second part, I will show our simulation of tidally induced gravity waves and study their properties at the stellar center. The nonlinearity of waves can lead to wave damping and breaking and transfer angular momentum to the background mean flow. This wave-mean flow interaction is studied both with direct hydro simulations and the quasi-linear approximation, and it has significant implications on the fate of exoplanets around solar-type stars.
Zhao Guo is currently a research associate at the Department of Applied Math and Theoretical Physics, University of Cambridge. He obtained his PhD from Georgia State University with a thesis title: Asteroseismology of Binary Stars and Applications of Bayesian Inference Tools. Previously, He was the postdoc scholar at Copernicus Astronomical Center, Poland and Pennsylvania State University, USA. He has broad research interests, including asteroseismology, close binary stars, nonlinear dynamical systems and astrophysical fluid dynamics.