The Aligned Orbit of the Eccentric Proto Hot Jupiter TOI-3362b

TL;DR

This study measures the orbit and spin-orbit alignment of proto-hot Jupiter TOI-3362b, providing insights into high-eccentricity migration mechanisms and the system's potential distant companion.

Contribution

It presents high-precision radial velocity measurements of TOI-3362b, constraining its eccentricity and obliquity, and discusses implications for migration theories and unseen companions.

Findings

TOI-3362b has a high eccentricity of 0.720.

The planet's orbit is nearly aligned with the star's spin axis.

A distant companion beyond 5 au may explain the system's architecture.

Abstract

High-eccentricity tidal migration predicts the existence of highly eccentric proto-hot Jupiters on the "tidal circularization track," meaning that they might eventually become hot Jupiters, but that their migratory journey remains incomplete. Having experienced moderate amounts of the tidal reprocessing of their orbital elements, proto-hot Jupiters systems can be powerful test beds for the underlying mechanisms of eccentricity growth. Notably, they may be used for discriminating between variants of high-eccentricity migration, each predicting a distinct evolution of misalignment between the star and the planet's orbit. We constrain the spin-orbit misalignment of the proto-hot Jupiter TOI-3362b with high-precision radial velocity observations using ESPRESSO at VLT. The observations reveal a sky-projected obliquity $\lambda = 1.2_{-2.7}^{+2.8}$ deg and constrain the orbital eccentricity to $e=0.720 \pm 0.016$, making it one of the most eccentric gas giants for which the obliquity has been measured. The large eccentricity and the striking orbit alignment of the planet suggest that ongoing coplanar high-eccentricity migration driven by a distant companion is a possible explanation for the system's architecture. This distant companion would need to reside beyond 5 au at 95% confidence to be compatible with the available radial velocity observations.