We report the discovery and characterisation of a super-Earth and a sub-Neptune-sized planet transiting the bright (K=8.8), quiet and nearby (37pc) 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 (Mexico). We also include additional ground-based follow-up photometryas well as high-resolution spectroscopy and high-angular imaging observations. The inner, larger planet has a radius of \(R=2.37^{+0.16}_{-0.12}\) \(R_\oplus\) and an orbital period of 10.9 days. The outer, smaller planet has a radius of \(R=1.56^{+0.15}_{-0.13}\) \(R_\oplus\) on a 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 planet masses and eccentricities. We find planetary masses of \(M_p=13.5^{+11.0}_{-9.0}\) \(M_\oplus\) (\(<36.8\) \(M_\oplus\) at 2-\(\sigma\))for TOI-1266 b and \(2.2^{2.0}_{-1.5}\) \(M_\oplus\) (\(<5.7\) \(M_\oplus\) at 2-\(\sigma\)) for TOI-1266 c. We constrain the orbital eccentricities to \(0.09^{+0.06}_{-0.05}\) (\(<0.21\) at 2-\(\sigma\)) for TOI-1266 band \(0.04\pm 0.03\) (\(<0.10\) at 2-\(\sigma\)) for TOI-1266 c. The equilibrium temperatures of both planets are of \(413\pm20\) K and \(344\pm16\) 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 to the planetary system architecture and favourable planet-to-star radii ratios makes TOI-1266 an exquisite system for detailed characterisation. TOI-1266 represents an opportunity, near the bottom of the main sequence, to study the interiors and atmospheres of two planetsbelonging to the same system that have experienced distinct evolution pathways.
Authors: B.-O. Demory, F.J. Pozuelos, Y. Gómez Maqueo Chew, L. Sabin, R. Petrucci, U. Schroffenegger, S.L. Grimm, M. Sestovic, M. Gillon, J. McCormac, K. Barkaoui, W. Benz, A. Bieryla, F. Bouchy, A. Burdanov, K.A. Collins, J. de Wit, C.D. Dressing, L.J. Garcia, S. Giacalone, P. Guerra, J. Haldemann, K. Heng, E. Jehin, E. Jofré, S.R. Kane, J. Lillo-Box, V. Maigné, C. Mordasini, B. M. Morris, P. Niraula, D. Queloz, B.V. Rackham, A.B. Savel, A. Soubkiou, G. Srdoc, K.G. Stassun, R. Zambelli, G. Ricker, D.W. Latham, S. Seager, J.N. Winn, J.M. Jenkins, T. Calvario-Velásquez, J.A. Franco Herrera, E. Colorado, E.O. Cadena Zepeda, L. Figueroa, A.M. Watson, E.E. Lugo-Ibarra, L. Carigi, G. Guisa, J. Herrera, G. Sierra Díaz, J.C. Suárez, D. Barrado, N.M. Batalha, Z. Benkhaldoun, A. Chontos, F. Dai, Z. Essack, M. Ghachoui, C.X. Huang, D. Huber, H. Isaacson, J.J. Lissauer, M. Morales-Calderón, P. Robertson, A. Roy, J.D. Twicken, A. Vanderburg, and L.M. Weiss