14 Her: a likely case of planet-planet scattering

TL;DR

This study precisely characterizes the orbits of two giant planets around 14 Herculis, revealing non-coplanar orbits and suggesting planet-planet scattering as the likely formation mechanism.

Contribution

We combined radial velocity data with Gaia-Hipparcos proper motion measurements to determine the masses and inclinations of both planets, providing new insights into their orbital architecture.

Findings

The b planet has a mass of approximately 9.1 Jupiter masses and an inclination of about 33 degrees.

The c planet has a mass of approximately 6.9 Jupiter masses and an inclination near 101 degrees.

The planets' orbits are strongly non-coplanar, supporting a scattering formation scenario.

Abstract

In this Letter, we measure the full orbital architecture of the two-planet system around the nearby K0 dwarf 14 Herculis. 14 Her (HD 145675, HIP 79248) is a middle-aged ($4.6^{+3.8}_{-1.3}$ Gyr) K0 star with two eccentric giant planets identified in the literature from radial velocity (RV) variability and long-term trends. Using archival RV data from Keck/HIRES in concert with \textit{Gaia-Hipparcos} acceleration in the proper motion vector for the star, we have disentangled the mass and inclination of the b planet to ${9.1}_{-1.1}^{+1.0}$ $M_\mathrm{Jup}$ and ${32.7}_{-3.2}^{+5.3}$ degrees. Despite only partial phase coverage for the c planet's orbit, we are able to constrain its mass and orbital parameters as well to ${6.9}_{-1.0}^{+1.7}$ $M_\mathrm{Jup}$ and ${101}_{-33}^{+31}$ degrees. We find that coplanarity of the b and c orbits is strongly disfavored. Combined with the age of the system and the comparable masses of its planets, this suggests that planet-planet scattering may be responsible for the current configuration of the system.