GJ 251 RVs & candidate exoplanet in habitable zone

Using high-precision Habitable-zone Planet Finder and NEID RVs, in conjunction with archival RVs from the Keck I High Resolution Echelle Spectrometer, the Calar Alto High-resolution Search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrograph, and the Spectropolarimetre Infrarouge, we improve the measured parameters of the known planet, GJ 251 b (P_b_=14.2370days; msin(i)=3.85_-0.33_^+0.35^M_{Earth}_), and we significantly constrain the minimum mass of GJ 251 c, placing it in a plausibly terrestrial regime (P_c_=53.647+/-0.044days; msin(i_c_)=3.84+/-0.75M_{Earth}_).

Using activity mitigation techniques that leverage chromatic information content, we perform a color-dependent analysis of the system and a detailed comparison of more than 50 models that describe the nature of the planets and stellar activity in the system. Due to GJ 251's proximity to Earth (5.5pc), next generation, 30m class telescopes will likely be able to image terrestrial planets in GJ 251's HZ. In fact, GJ 251 c is currently the best candidate for terrestrial, HZ planet imaging in the northern sky.