2022AJ....163..225T

We report the discovery of two transiting planets around the bright (V = 9.9 mag) main-sequence F7 star TOI-1670 by the Transiting Exoplanet Survey Satellite. TOI-1670 b is a sub-Neptune (R_b=2.06_–0.15^+0.19 R_⊕) on a 10.9 day orbit, and TOI-1670 c is a warm Jupiter (R_c = 0.987_–0.025^+0.025 R_Jup) on a 40.7 day orbit. Using radial velocity observations gathered with the Tull Coude Spectrograph on the Harlan J. Smith telescope and HARPS-N on the Telescopio Nazionale Galileo, we find a planet mass of M_c= 0.63_–0.08^+0.09 M_Jup for the outer warm Jupiter, implying a mean density of ρ_c=0.81_–0.11^+0.13 g cm^–3. The inner sub-Neptune is undetected in our radial velocity data (M_b < 0.13 M_Jup at the 99% confidence level). Multiplanet systems like TOI-1670 hosting an outer warm Jupiter on a nearly circular orbit e_c=0.09-0.04_^+0.05) and one or more inner coplanar planets are more consistent with "gentle" formation mechanisms such as disk migration or in situ formation rather than high-eccentricity migration. Of the 11 known systems with a warm Jupiter and a smaller inner companion, eight (73%) are near a low-order mean-motion resonance, which can be a signature of migration. TOI-1670 joins two other systems (27% of this subsample) with period commensurabilities greater than 3, a common feature of in situ formation or halted inward migration. TOI-1670 and the handful of similar systems support a diversity of formation pathways for warm Jupiters.