Thursday, September 17, 2015

Orbital Decay of hot Jupiters

Orbital decay of hot Jupiters due to nonlinear tidal dissipation within solar-type hosts


Essick et al


We study the orbital evolution of hot Jupiters due to the excitation and damping of tidally driven g-modes within solar-type host stars. Linearly resonant g-modes (the dynamical tide) are driven to such large amplitudes in the stellar core that they excite a sea of other g-modes through weakly nonlinear interactions. By solving the dynamics of large networks of nonlinearly coupled modes, we show that the nonlinear dissipation rate of the dynamical tide is several orders of magnitude larger than the linear dissipation rate. As a result, we find that the orbits of planets with mass Mp greater than 0.5MJ and period P less than 2 days decay on timescales that are small compared to the main-sequence lifetime of their solar-type hosts. This corresponds to stellar tidal quality factors Q′∗≃105−106 for this range of Mp and P. Our results imply that there are ≃10 currently known exoplanetary systems, including WASP-19b and HAT-P-36-b, with orbital decay timescales shorter than a Gyr. Rapid, tide induced orbital decay may explain the observed paucity of planets with Mp greater than MJ and P less than 2 days around solar-type hosts and could generate detectable transit-timing variations in the near future.

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