RV and TTV Measurements of Two Transiting Long-Period Giants around TOI-4600

Abstract

TOI-4600b and c, originally identified by the Transiting Exoplanet Survey Satellite (TESS) and reported by I. Mireles et al. (2023), are a rare pair of transiting long-period giant planets (${\mathrm{P}}_{\mathrm{b}}=82.7$ days, ${\mathrm{P}}_{\mathrm{c}}=482.8$ days) orbiting an early K dwarf. In this work, we refine the orbital parameters of the TOI-4600 system by combining new TESS photometry, ground-based transit follow-up, and radial velocity (RV) observations from MAROON-X. We obtain improved constraints on planetary masses and eccentricities, and update other parameters, such as the stellar age. For TOI-4600b, we measure a mass of $M_p=74.7_{-4.4}^{+4.7}{M}_{\oplus }$ and an eccentricity of $e=0.153_{-0.018}^{+0.020}$, and $M_p=212.53_{-13.03}^{+13.26}{M}_{\oplus }$ and $e=0.219_{-0.018}^{+0.015}$ for TOI-4600c. We find significant transit timing variations (TTV) in both planets, with semi-amplitudes of approximately $1$\,hr. We derive Transit Spectroscopy Metric values of 16.87 for TOI-4600b and 10.09 for TOI-4600c, indicating that both planets are promising JWST targets for studying the atmospheres of temperate and cold Jupiters, a relatively poorly characterized sample thus far. These updated parameters and TTV ephemerides are important for planning and interpreting future photometric, spectroscopic, and dynamical studies of the TOI-4600 system.

Submitted to AJ, 23 pages, 6 figures, 7 tables