Measurement of the Nodal Precession of WASP-33 b via Doppler Tomography

TL;DR

This study measures the nodal precession of exoplanet WASP-33 b using Doppler tomography, revealing changes in its orbit over six years and providing insights into the star's gravitational quadrupole moment.

Contribution

First direct measurement of nodal precession for an exoplanet transiting a single star using Doppler tomography techniques.

Findings

Measured precession rates of the planet's orbit.

Detected change in the planet's transit path over six years.

Constrained the stellar gravitational quadrupole moment.

Abstract

We have analyzed new and archival time series spectra taken six years apart during transits of the hot Jupiter WASP-33 b, and spectroscopically resolved the line profile perturbation caused by the Rossiter-McLaughlin effect. The motion of this line profile perturbation is determined by the path of the planet across the stellar disk, which we show to have changed between the two epochs due to nodal precession of the planetary orbit. We measured rates of change of the impact parameter and the sky-projected spin-orbit misalignment of $db/dt=-0.0228_{-0.0018}^{+0.0050}$ yr$^{-1}$ and $d\lambda/dt=-0.487_{-0.076}^{+0.089}$~$^{\circ}$ yr$^{-1}$, respectively, corresponding to a rate of nodal precession of $d\Omega/dt=0.373_{-0.083}^{+0.031}$~$^{\circ}$ yr$^{-1}$. This is only the second measurement of nodal precession for a confirmed exoplanet transiting a single star. Finally, we used the rate of precession to set limits on the stellar gravitational quadrupole moment of $9.4\times10^{-5}<J_2<6.1\times10^{-4}$.