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

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

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 Tillinghast Reflector Echelle Spectrograph (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°) and HAT-P-56b (8° ± 2°). 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 supersynchronous, spin-orbit aligned states, where the rotation periods of the host stars are faster than the orbital periods of the planets.

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.