A Pair of Warm Saturn-mass Planets near the 2:1 Mean Motion Resonance around TOI-3850

Abstract

Warm Jupiters, with orbital periods of $10$--$200\mathrm{days}$ and radii exceeding $8R_{\oplus }$, are a relatively understudied class of exoplanets occupying the parameter space between hot Jupiters and more widely separated, colder Jupiter analogs. In this work, we report the detection of a multi-planet warm Jupiter system around TOI-3850 (TIC-143008050), a moderately active, near-solar metallicity G0 dwarf star observed by TESS in Sectors 15, 21, 41, 48 and 75. Initially, a single candidate planet was discovered by TESS, displaying transit timing variations (TTVs) with an amplitude of $\sim 1\mathrm{hr}$ and a super-period of $513\mathrm{days}$. Through a combination of transit photometry, radial velocity observations with MAROON-X, and TTV modeling, we identify two planets: TOI-3850 b $(P_b=14.484\pm 0.002\mathrm{days},M_b=112\pm 20M_{\oplus },e_b=0.018\pm 0.008,R_b=12.07\pm 0.09R_{\oplus },T_{\mathrm{eq}}=841\pm 10\mathrm{K})$, a transiting warm Jupiter, and TOI-3850 c $(P_c=29.85\pm 0.01\mathrm{days},M_c=90\pm 15M_{\oplus },e_c<0.015,T_{\mathrm{eq}}=661\pm 7\mathrm{K})$, a non-transiting, Saturn-mass companion. The two planets lie wide of the 2:1 mean motion resonance $(P_c/P_b\approx 2.06)$, consistent with a formation history involving disk-driven migration. $N$-body integrations indicate that TOI-3850 c may begin to transit on decadal timescales, while TOI-3850 b remains a promising target for follow-up atmospheric characterization.

25 pages, 13 figures, 7 tables, submitted AAS journals. Comments welcome