Work

Photodynamical analysis of the TOI-4504 system: Orbital precession brings planet d into transit to reveal its deeply resonant state and similarity to GJ 876

Year: 2026

Type: article

Abstract: The K-dwarf TOI-4504 hosts two giant planets in a 2:1 mean-motion resonance (MMR) with orbital periods of 41.3 days (planet d) and 82.8 days (planet c). They exhibit among the largest known absolute transit-timing variations, with respective peak-to-node amplitudes up to 5 and 3 days. Newer TESS data show that the previously nontransiting planet d has now precessed into transiting. We have derived updated system parameters and find significant discrepancies with the discovery paper. The revised parameters place planets d and c deep in the resonance and close to or in the fully-relaxed limit-cycle state, with the resonant and secular modes interfering nonlinearly to induce nonzero relaxed free eccentricities which precess at the same rate as the forced eccentricities and the longitude of conjunctions. In turn, this enabled the precise measurement of the full eccentricities and apsidal angles. We discuss the predictions of linear theory and how it can be used to understand the true state of the system revealed by N -body integrations, and more generally why the posteriors of systems more compact than 2:1 tend to suffer from significant eccentricity degeneracy. We show that the extraordinary dynamical states of the giant pairs orbiting TOI-4504 and the M-dwarf GJ 876 are remarkably similar, in spite of the significant difference in their host-star masses. Finally, we discuss the implications for damping timescales during the relatively gentle formation process of type II migration.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202658959