Orbital Orientations of Exoplanets: HAT-P-4b is Prograde and HAT-P-14b is Retrograde

TL;DR

This study measures the orbital orientations of two exoplanets, HAT-P-4b and HAT-P-14b, revealing a prograde and a retrograde orbit respectively, and discusses implications for planetary system dynamics.

Contribution

First measurements of the Rossiter-McLaughlin effect for these systems, showing diverse orbital alignments and discovering a potential third body in the HAT-P-4 system.

Findings

HAT-P-4b is prograde with a near-aligned orbit.

HAT-P-14b is retrograde with a significant misalignment.

A third body was detected in the HAT-P-4 system.

Abstract

We present observations of the Rossiter-McLaughlin effect for two exoplanetary systems, revealing the orientations of their orbits relative to the rotation axes of their parent stars. HAT-P-4b is prograde, with a sky-projected spin-orbit angle of lambda = -4.9 +/- 11.9 degrees. In contrast, HAT-P-14b is retrograde, with lambda = 189.1 +/- 5.1 degrees. These results conform with a previously noted pattern among the stellar hosts of close-in giant planets: hotter stars have a wide range of obliquities and cooler stars have low obliquities. This, in turn, suggests that three-body dynamics and tidal dissipation are responsible for the short-period orbits of many exoplanets. In addition, our data revealed a third body in the HAT-P-4 system, which could be a second planet or a companion star.