Kavli Affiliate: Saul Rappaport
| First 5 Authors: Jim Fuller, Saul Rappaport, Rahul Jayaraman, Don Kurtz, Gerald Handler
| Summary:
Stars in close binaries are tidally distorted, and this has a strong effect
on their pulsation modes. We compute the mode frequencies and geometries of
tidally distorted stars using perturbation theory, accounting for the effects
of the Coriolis force and the coupling between different azimuthal orders $m$
of a multiplet induced by the tidal distortion. For tidally coupled dipole
pressure modes, the tidal coupling dominates over the Coriolis force and the
resulting pulsations are “triaxial", with each of the three modes in a
multiplet “tidally tilted" to be aligned with the one of the three principal
axes of the star. The observed amplitudes and phases of the dipole modes
aligned orthogonal to the spin axis are modulated throughout the orbit,
producing doublets in the power spectrum that are spaced by exactly twice the
orbital frequency. Quadrupole modes have similar but slightly more complex
behavior. This amplitude modulation allows for mode identification which can
potentially enable detailed asteroseismic analyses of tidally tilted pulsators.
Pressure modes should exhibit this behavior in stellar binaries close enough to
be tidally synchronized, while gravity modes should remain aligned with the
star’s spin axis. We discuss applications to various types of pulsating stars,
and the relationship between tidal tilting of pulsations and the
“single-sided" pulsations sometimes observed in very tidally distorted stars.
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