Influence of Modeling Assumptions on the Inferred Dynamical State of Resonant Systems: A Case Study of the HD 45364 System

TL;DR

This study examines how modeling assumptions influence the inferred dynamical state of the HD 45364 planetary system, demonstrating that different priors can lead to similar observational fits but different dynamical interpretations.

Contribution

The paper shows that the inferred resonance state of HD 45364 depends on prior assumptions and that smooth migration models can reproduce its current configuration within certain parameters.

Findings

Orbital solutions consistent with 3:2 MMR fit RV data well.

Migration to resonance is plausible with specific damping timescale ratios.

Dynamical interactions can constrain planetary masses within a factor of 1.5.

Abstract

Planetary systems exhibiting mean-motion resonances (MMRs) offer unique opportunities to study the imprint of disk-induced migration on the orbital architectures of planetary systems. The HD 45364 system, discovered via the radial velocity (RV) method to host two giant planets in a 3:2 MMR, has been the subject of several studies attempting to reconstruct the system's orbital migration history based on its present-day resonant configuration. Recently, Li et al. (2022) called into question the system's residence in the 3:2 MMR based on a revised orbital solution derived from an expanded set of RV observations that extend the time baseline of the original discovery data by over a decade. However, we show that inferences about the planets' dynamical state with respect to the 3:2 MMR are sensitive to the particular prior assumptions adopted in the orbital modeling. Using $N$-body dynamical models, we show that orbital solutions constrained to reside deep in the 3:2 MMR fit the RV data with a similar quality to unconstrained orbital solutions. We conclude that the RV observations of HD 45364 are consistent with orbital configurations produced by smooth migration and resonance capture. We further show that past convergent orbital migration can reproduce the system's present-day orbital configuration provided that the ratio of migration to eccentricity damping timescales, $K$, was in the range $11\lesssim K \lesssim 144$. We also find that dynamical interactions in the system can break the usual mass-inclination degeneracy inherent to Keplerian models of RV observations and constrain the planets' absolute masses to within a factor of $\sim1.5$.