A Misaligned Prograde Orbit for Kepler-13 Ab via Doppler Tomography

TL;DR

This study uses Doppler tomography to confirm Kepler-13 Ab as a hot Jupiter with a prograde, misaligned orbit, revealing a significant discrepancy with previous measurements and providing insights into planetary migration.

Contribution

The paper demonstrates the application of Doppler tomography for direct confirmation and orbit characterization of a transiting planet around a rapidly rotating star, revealing a misaligned orbit.

Findings

Confirmed Kepler-13 Ab as a hot Jupiter using Doppler tomography.

Measured a spin-orbit misalignment of 58.6 degrees, differing from previous estimates.

Placed an upper mass limit of 0.75 solar masses on Kepler-13 C.

Abstract

Transiting planets around rapidly rotating stars are not amenable to precise radial velocity observations, such as are used for planet candidate validation, as they have wide, rotationally broadened stellar lines. Such planets can, however, be observed using Doppler tomography, wherein the stellar absorption line profile distortions during transit are spectroscopically resolved. This allows the validation of transiting planet candidates and the measurement of the stellar spin-planetary orbit (mis)alignment, an important statistical probe of planetary migration processes. We present Doppler tomographic observations which provide a direct confirmation of the hot Jupiter Kepler-13 Ab, and also show that the planet has a prograde, misaligned orbit, with lambda = 58.6 +/- 2.0 degrees. Our measured value of the spin-orbit misalignment is in significant disagreement with the value of lambda = 23 +/- 4 degrees previously measured by Barnes et al. (2011) from the gravity-darkened Kepler lightcurve. We also place an upper limit of 0.75 solar masses (95% confidence) on the mass of Kepler-13 C, the spectroscopic companion to Kepler-13 B, the proper motion companion of the planet host star Kepler-13 A.