A super-Earth and a sub-Neptune orbiting the bright, quiet M3 dwarf TOI-1266

Abstract

We report the discovery and characterisation of a super-Earth and a sub-Neptune transiting the bright (K = 8:8), quiet, and nearby (37 pc) M3V dwarf TOI-1266. We validate the planetary nature of TOI-1266 b and c using four sectors of TESS photometry and data from the newly-commissioned 1-m SAINT-EX telescope located in San Pedro Mártir (México). We also include additional groundbased follow-up photometry as well as high-resolution spectroscopy and high-angular imaging observations. The inner, larger planet has a radius of R = 2:37+0:16 -0:12 R and an orbital period of 10.9 days. The outer, smaller planet has a radius of R = 1:56+0:15 -0:13 R on an 18.8-day orbit. The data are found to be consistent with circular, co-planar and stable orbits that are weakly influenced by the 2:1 mean motion resonance. Our TTV analysis of the combined dataset enables model-independent constraints on the masses and eccentricities of the planets. We find planetary masses of Mp = 13:5+11:0 -9:0 M (<36:8 M at 2- ) for TOI-1266 b and 2:2+2:0 -1:5 M (<5:7 M at 2- ) for TOI-1266 c. We find small but non-zero orbital eccentricities of 0:09+0:06 -0:05 (<0:21 at 2- ) for TOI-1266 b and 0:04 0:03 (<0:10 at 2- ) for TOI-1266 c. The equilibrium temperatures of both planets are of 413 20 and 344 16 K, respectively, assuming a null Bond albedo and uniform heat redistribution from the day-side to the night-side hemisphere. The host brightness and negligible activity combined with the planetary system architecture and favourable planet-to-star radii ratios makes TOI-1266 an exquisite system for a detailed characterisation.