Spin orbit alignment for KELT-7b and HAT-P-56b via Doppler tomography with TRES

TL;DR

This study uses Doppler tomography to analyze the spin-orbit alignment of two hot-Jupiter systems around rapidly rotating F-dwarfs, revealing aligned geometries and suggesting primordial configurations unaffected by tidal interactions.

Contribution

First Doppler tomographic analysis of KELT-7b and HAT-P-56b, demonstrating aligned spin-orbit geometries in rapidly rotating host stars.

Findings

KELT-7b has a spin-orbit angle of 2.7 +/- 0.6 degrees.

HAT-P-56b has a spin-orbit angle of 8 +/- 2 degrees.

Host stars are among the fastest rotating known planet hosts.

Abstract

We present Doppler tomographic analyses for the spectroscopic transits of KELT-7b and HAT-P-56b, two hot-Jupiters orbiting rapidly rotating F-dwarf host stars. These include analyses of archival TRES observations for KELT-7b, and a new TRES transit observation of HAT-P-56b. We report spin-orbit aligned geometries for KELT-7b (2.7 +/- 0.6 deg) and HAT-P-56b (8 +/- 2 deg). The host stars KELT-7 and HAT-P-56 are among some of the most rapidly rotating planet-hosting stars known. We examine the tidal re-alignment model for the evolution of the spin-orbit angle in the context of the spin rates of these stars. We find no evidence that the rotation rates of KELT-7 and HAT-P-56 have been modified by star-planet tidal interactions, suggesting that the spin-orbit angle of systems around these hot stars may represent their primordial configuration. In fact, KELT-7 and HAT-P-56 are two of three systems in super-synchronous, spin-orbit aligned states, where the rotation periods of the host stars are faster than the orbital periods of the planets.