@misc{10481/70908,
year = {2021},
month = {9},
url = {http://hdl.handle.net/10481/70908},
abstract = {Context. Large sub-Neptunes are uncommon around the coolest stars in the Galaxy and are rarer still around those that are metal-poor. However, owing to the large planet-to-star radius ratio, these planets are highly suitable for atmospheric study via transmission spectroscopy in the infrared, such as with JWST. Aims. Here we report the discovery and validation of a sub-Neptune orbiting the thick-disk, mid-M dwarf star TOI-2406. The star's low metallicity and the relatively large size and short period of the planet make TOI-2406 b an unusual outcome of planet formation, and its characterisation provides an important observational constraint for formation models. Methods. We first infer properties of the host star by analysing the star's near-infrared spectrum, spectral energy distribution, and Gaia parallax. We use multi-band photometry to confirm that the transit event is on-target and achromatic, and we statistically validate the TESS signal as a transiting exoplanet. We then determine physical properties of the planet through global transit modelling of the TESS and ground-based time-series data. Results. We determine the host to be a metal-poor M4 V star, located at a distance of 56 pc, with properties T-eff = 3100 +/- 75 K, M-* = 0.162 +/- 0.008M(circle dot), R-* = 0.202 +/- 0.011R(circle dot), and [Fe/H] = -0.38 +/- 0.07, and a member of the thick disk. The planet is a relatively large sub-Neptune for the M-dwarf planet population, with R-p = 2.94 +/- 0.17R(circle plus) and P= 3.077 d, producing transits of 2% depth. We note the orbit has a non-zero eccentricity to 3 sigma, prompting questions about the dynamical history of the system. Conclusions. This system is an interesting outcome of planet formation and presents a benchmark for large-planet formation around metal-poor, low-mass stars. The system warrants further study, in particular radial velocity follow-up to determine the planet mass and constrain possible bound companions. Furthermore, TOI-2406 b is a good target for future atmospheric study through transmission spectroscopy. Although the planet's mass remains to be constrained, we estimate the S/N using amass-radius relationship, ranking the system fifth in the population of large sub-Neptunes, with TOI-2406 b having a much lower equilibrium temperature than other spectroscopically accessible members of this population.},
organization = {Heising-Simons Foundation},
organization = {Programa de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT)},
organization = {Universidad Nacional Autonoma de Mexico	IG-101321},
organization = {Swiss National Science Foundation (SNSF)},
organization = {European Commission	PP00P2-163967	
PP00P2-190080	
P2BEP2_195285},
organization = {MIT's Kavli Institute as a Juan Carlos Torres Fellow},
organization = {European Research Council (ERC)	nffi 803193/BEBOP},
organization = {MERAC foundation},
organization = {UK Research & Innovation (UKRI)},
organization = {Science & Technology Facilities Council (STFC)},
organization = {Science and Technology Development Fund (STDF)	nffi ST/S00193X/1},
organization = {MIT's Kavli Institute as a Kavli postdoctoral fellow},
organization = {Swiss National Science Foundation (SNSF)},
organization = {Australian Research Council},
organization = {Fonds de la Recherche Scientifique - FNRS	FRFC 2.5.594.09.F},
organization = {Swiss National Science Foundation (SNSF)},
organization = {French Community of Belgium in the context of the FRIA Doctoral Grant},
organization = {NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center},
organization = {NASA's Science Mission Directorate},
organization = {National Aeronautics and Space Administration under the Exoplanet Exploration Program},
organization = {TESS GI program	G03274},
organization = {National Science Foundation (NSF)},
organization = {Earths in Other Solar Systems Project (EOS)},
organization = {Alien Earths - NASA	NNX15AD94G	
80NSSC21K0593},
organization = {High-Resolution Imaging instrument Zorro (Gemini program)	GS-2020B-LP-105},
organization = {NASA Exoplanet Exploration Program},
organization = {National Aeronautics & Space Administration (NASA)},
organization = {National Science Foundation (NSF)},
publisher = {EDP Sciences},
keywords = {Planets and satellites: detection},
keywords = {Stars: individual: TOI-2406},
keywords = {Techniques: photometric},
title = {A large sub-Neptune transiting the thick-disk M4 V TOI-2406},
doi = {10.1051/0004-6361/202141277},
author = {Wells, R. D. and Dévora Pajares, Martín},
}