Phot. follow-up of TOI-2015 & discovery of TOI-2015b

We characterize the planet's properties using Transiting Exoplanet Survey Satellite (TESS) photometry, precise near-infrared radial velocities (RVs) with the Habitable-zone Planet Finder Spectrograph, ground-based photometry, and high-contrast imaging. A joint photometry and RV fit yields a radius Rp=3.37_-0.20_^+0.15^R_{Earth}_, mass mp=16.4_-4.1_^+4.1^M_{Earth}_, and density {rho}p=2.32_-0.37_^+0.38^g/cm^3^ for TOI-2015 b, suggesting a likely volatile-rich planet.

The young, active host star has a rotation period of Prot=8.7+/-0.9days and associated rotation-based age estimate of 1.1+/-0.1Gyr. Though no other transiting planets are seen in the TESS data, the system shows clear TTVs of super-period Psup~430days and amplitude ~100min. After considering multiple likely period-ratio models, we show an outer planet candidate near a 2:1 resonance can explain the observed TTVs while offering a dynamically stable solution.