Spin-Orbit Alignment for the Eccentric Exoplanet HD 147506b

TL;DR

This study measures the spin-orbit alignment of the eccentric exoplanet HD 147506b using the Rossiter-McLaughlin effect, finding alignment within 14 degrees, which challenges some migration theories.

Contribution

First spectroscopic measurement of the spin-orbit alignment for HD 147506b, providing insights into its migration history.

Findings

Stellar and orbital axes are aligned within 14 degrees.

No evidence for significant orbital tilt or misalignment.

Results suggest a different migration pathway than scattering or Kozai oscillations.

Abstract

The short-period exoplanet HD 147506b (also known as HAT-P-2b) has an eccentric orbit, raising the possibility that it migrated through planet-planet scattering or Kozai oscillations accompanied by tidal dissipation. Either of these scenarios could have significantly tilted the orbit relative to the host star's equatorial plane. Here we present spectroscopy of a transit of HD 147506b, and assess the spin-orbit alignment via the Rossiter-McLaughlin effect. We find the sky projections of the stellar spin axis and orbital axis to be aligned within 14 deg. Thus we find no corroborating evidence for scattering or Kozai migration, although these scenarios cannot be ruled out with the present data.