Tidal Response and Shape of Hot Jupiters
We study the response of hot Jupiters to a static tidal perturbation using the Concentric MacLaurin Spheroid (CMS) method. For strongly irradiated planets, we first performed radiative transfer calculations to relate the planet's equilibrium temperature, T_eq, to its interior entropy. We then determined the gravity harmonics, shape, moment of inertia, and the static Love numbers for a range of two-layer interior models that assume a rocky core plus a homogeneous and isentropic envelope composed of hydrogen, helium, and heavier elements. We identify general trends and then study HAT-P-13b, the WASP planets 4b, 12b, 18b, 103b, and 121b, as well as Kepler-75b and CoRot-3b. We compute the Love numbers, k_nm, and transit radius correction, Delta R, which we compare with predictions in the literature. We find that the Love number, k_22, of tidally locked giant planets cannot exceed the value 0.6, and that the high T_eq consistent with strongly irradiated hot Jupiters tend %lead to further lower k_22. While most tidally locked planets are well described by a linear-regime response of k_22 = 3 J_2/q_0 (where q_0 is the rotation parameter of the gravitational potential), for extreme cases such as WASP-12b, WASP-103b and WASP-121b, nonlinear effects can account for over 10% of the predicted k_22. k_22 values larger than 0.6, as they have been reported for planets WASP-4b and HAT-P13B, cannot result from a static tidal response without extremely rapid rotation, and thus are inconsistent with their expected tidally-locked state.