Accurate characterization of the stellar and orbital parameters of the exoplanetary system WASP-33 b from orbital dynamics

Original · EN

By using the most recently published Doppler tomography measurements and accurate theoretical modeling of the oblateness-driven orbital precessions, we tightly constrain some of the physical and orbital parameters of the planetary system hosted by the fast rotating star WASP-33. In particular, the measurements of the orbital inclination i p to the plane of the sky and of the sky-projected spin-orbit misalignment λ at two epochs about six years apart allowed for the determination of the longitude of the ascending node Ω and of the orbital inclination I to the apparent equatorial plane at the same epochs. As a consequence, average rates of change Ω exp, I exp of this two orbital elements, accurate to a ≈ 10⁻² deg yr⁻¹ level, were calculated as well. By comparing them to general theoretical expressions Ωⱼ₂, Iⱼ₂ for their precessions induced by an oblate star whose symmetry axis is arbitrarily oriented, we were able to determine the angle i⋆ between the line of sight the star's spin S⋆ and its first even zonal harmonic J₂⋆ obtaining i⋆ = 142⁺¹⁰₋₁₁ deg, J₂⋆ = (2.1⁺⁰.⁸₋₀.₅)× 10⁻⁴. As a by-product, the angle between S⋆ and the orbital angular momentum L is as large as about ψ≈ 100 deg (ψ²⁰⁰⁸ = 99⁺⁵₋₄ deg, ψ²⁰¹⁴ = 103⁺⁵₋₄ deg), and changes at a rate ψ= 0.7⁺¹.⁵₋₁.₆ deg yr⁻¹. The predicted general relativistic Lense-Thirring precessions, or the order of ≈ 10⁻³ deg yr⁻¹, are, at present, about one order of magnitude below the measurability threshold.