TESS-Keck Survey. XIII. TOI-1272 radial velocity

We identified the eccentricity of the inner planet, with an orbital period of 3.3days and Rp,b=4.1{+/-}0.2R{Earth}, based on a mismatch between the observed transit duration and the expected duration for a circular orbit. Using ground-based radial velocity (RV) measurements from the HIRES instrument at the Keck Observatory, we measured the mass of TOI-1272b to be Mp,b=25{+/-}2M{Earth}.

We also confirmed a high eccentricity of eb=0.34{+/-}0.06, placing TOI-1272b among the most eccentric well-characterized sub-Jovians. We used these RV measurements to also identify a non-transiting outer companion on an 8.7day orbit with a similar mass of Mp,csin(i)=27{+/-}3M{Earth} and ec<~0.35. Dynamically stable planet-planet interactions have likely allowed TOI-1272b to avoid tidal eccentricity decay despite the short circularization timescale expected for a close-in eccentric Neptune.