Asteroseismic determination of obliquities of the exoplanet systems Kepler-50 and Kepler-65

TL;DR

This study uses asteroseismology to measure the obliquities of Kepler-50 and Kepler-65, revealing that both stars' rotation axes are nearly perpendicular to our line of sight and their planetary orbits are likely coplanar.

Contribution

First application of asteroseismology to determine stellar obliquities in systems with transiting planets and Sun-like stars, providing new insights into planetary system orientations.

Findings

Both stars have rotation axes nearly perpendicular to our line of sight.

Planetary orbits are likely coplanar and aligned with stellar rotation axes.

Stellar obliquities are constrained at the 1-sigma level to be above 0.97 and 0.91.

Abstract

Results on the obliquity of exoplanet host stars -- the angle between the stellar spin axis and the planetary orbital axis -- provide important diagnostic information for theories describing planetary formation. Here we present the first application of asteroseismology to the problem of stellar obliquity determination in systems with transiting planets and Sun-like host stars. We consider two systems observed by the NASA Kepler Mission which have multiple transiting small (super-Earth sized) planets: the previously reported Kepler-50 and a new system, Kepler-65, whose planets we validate in this paper. Both stars show rich spectra of solar-like oscillations. From the asteroseismic analysis we find that each host has its rotation axis nearly perpendicular to the line of sight with the sines of the angles constrained at the 1-sigma level to lie above 0.97 and 0.91, respectively. We use statistical arguments to show that coplanar orbits are favoured in both systems, and that the orientations of the planetary orbits and the stellar rotation axis are correlated.