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 ground-based follow-up photometry as well as high-resolution spectroscopy and high-angular imaging observations. The inner, larger planet has a radius of R = 2.37−0.12+0.16 R⊕ and an orbital period of 10.9 days. The outer, smaller planet has a radius of R = 1.56−0.13+0.15 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 = 13.5−9.0+11.0 M⊕ (<36.8 M⊕ at 2-σ) for TOI-1266 b and 2.2−1.5+2.0 M⊕ (<5.7 M⊕ at 2-σ) for TOI-1266 c. We find small but non-zero orbital eccentricities of 0.09−0.05+0.06 (<0.21 at 2-σ) for TOI-1266 b and 0.04 ± 0.03 (< 0.10 at 2-σ) 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.

The TESS Objects of Interest Catalog from the TESS Prime Mission

“…TOI 1266-The TOI 1266 system consists of two planets orbiting a nearby M dwarf star (Demory et al 2020;Stefansson et al 2020). The system is a key find because it will provide a strong test of photoevaporation models, as the outer planet (P = 18.8 days, = ) is very atypically smaller than the inner planet (P = 10.9 days, R p = 2.46 ± 0.08 R ⊕ ).…”

A Mini-Neptune and a Radius Valley Planet Orbiting the Nearby M2 Dwarf TOI-1266 in Its Venus Zone: Validation with the Habitable-zone Planet Finder

“…Lastly, we note that during the preparation of this manuscript, we became aware of an independent analysis of this system by Demory et al (2020). We note that all data analyses and interpretations presented here were performed independently from their work.…”

Development of the SPECULOOS exoplanet search project

“…The SPECULOOS Northern Observatory 47 (SNO) is currently composed of one telescope (Artemis), which is located at the Teide Observatory (Canary Islands, Spain) and operational since June 2019. SAINT-EX 48 (Search And characterIsatioN of Transiting EXoplanets) with one telescope in San Pedro Mártir observatory (Mexico) became operational in March 2019. Each of these observatories is devoting 70% of its usable observational time to the SPECULOOS survey.…”

“…Following-up photometric data from K2, using SSO and SNO observatories revealed the detection of π Earth, 47 a transiting Earth-sized (0.95 R ⊕ ) planet around the mid-M dwarf K2-315b in 57 pc distance, which is well suited for comparative terrestrial exoplanetology. The first discovery from the SAINT-EX observatory has been made possible by following-up the TESS transit candidate TOI-1266, 48 which revealed a system that hosts a super-Earth and a sub-Neptune around a M3 dwarf. The outer planet TOI-1266c has an irradiation level similar to that of Venus and is thus a favourable target for future atmospheric characterisation.…”