The multi-planet system TOI-421 -- A warm Neptune and a super puffy mini-Neptune transiting a G9 V star in a visual binary
Abstract
We report the discovery of a warm Neptune and a hot sub-Neptune transiting TOI-421 (BD-14 1137, TIC 94986319), a bright (V=9.9) G9 dwarf star in a visual binary system observed by the TESS space mission in Sectors 5 and 6. We performed ground-based follow-up observations -- comprised of LCOGT transit photometry, NIRC2 adaptive optics imaging, and FIES, CORALIE, HARPS, HIRES, and PFS high-precision Doppler measurements -- and confirmed the planetary nature of the 16-day transiting candidate announced by the TESS team. We discovered an additional radial velocity signal with a period of 5 days induced by the presence of a second planet in the system, which we also found to transit its host star. We found that the inner mini-Neptune, TOI-421b, has an orbital period of Pb =5.19672 +- 0.00049 days, a mass of Mb = 7.17 +- 0.66 Mearth and a radius of Rb = 2.68+0.19-0.18 Rearth, whereas the outer warm Neptune, TOI-421 c, has a period of Pc =16.06819 +- 0.00035 days, a mass of Mc = 16.42+1.06-1.04 Mearth, a radius of Rc = 5.09+0.16-0.15 Rearth and a density of rho_c =0.685+0.080-0.072 g cm-3 . With its characteristics the inner planet (rho_b=2.05+0.52-0.41 g cm-3) is placed in the intriguing class of the super-puffy mini-Neptunes. TOI-421b and TOI-421c are found to be well suitable for atmospheric characterization. Our atmospheric simulations predict significant Ly-alpha transit absorption, due to strong hydrogen escape in both planets, and the presence of detectable CH_4 in the atmosphere of TOI-421c if equilibrium chemistry is assumed.
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Cite
@article{arxiv.2004.10095,
title = {The multi-planet system TOI-421 -- A warm Neptune and a super puffy mini-Neptune transiting a G9 V star in a visual binary},
author = {Ilaria Carleo and Davide Gandolfi and Oscar Barragán and John H. Livingston and Carina M. Persson and Kristine W. F. Lam and Aline Vidotto and Michael B. Lund and Carolina Villarreal D'Angelo and Karen A. Collins and Luca Fossati and Andrew W. Howard and Daria Kubyshkina and Rafael Brahm and Antonija Oklopčić and Paul Mollière and Seth Redfield and Luisa Maria Serrano and Fei Dai and Malcolm Fridlund and Francesco Borsa and Judith Korth and Massimiliano Esposito and Matías R. Díaz and Louise Dyregaard Nielsen and Coel Hellier and Savita Mathur and Hans J. Deeg and Artie P. Hatzes and Serena Benatti and Florian Rodler and Javier Alarcon and Lorenzo Spina and Ângela R. G. Santos and Iskra Georgieva and Rafael A. García and Lucía González-Cuesta and George R. Ricker and Roland Vanderspek and David W. Latham and Sara Seager and Joshua N. Winn and Jon M. Jenkins and Simon Albrecht and Natalie M. Batalha and Corey Beard and Patricia T. Boyd and François Bouchy and Jennifer A. Burt and R. Paul Butler and Juan Cabrera and Ashley Chontos and David Ciardi and William D. Cochran and Kevin I. Collins and Jeffrey D. Crane and Ian Crossfield and Szilard Csizmadia and Diana Dragomir and Courtney Dressing and Philipp Eigmüller and Michael Endl and Anders Erikson and Nestor Espinoza and Michael Fausnaugh and Fabo Feng and Erin Flowers and Benjamin Fulton and Erica J. Gonzales and Nolan Grieves and Sascha Grziwa and Eike W. Guenther and Natalia M. Guerrero and Thomas Henning and Diego Hidalgo and Teruyuki Hirano and Maria Hjorth and Daniel Huber and Howard Isaacson and Matias Jones and Andrés Jordán and Petr Kabáth and Stephen R. Kane and Emil Knudstrup and Jack Lubin and Rafael Luque and Ismael Mireles and Norio Narita and David Nespral and Prajwal Niraula and Grzegorz Nowak and Enric Palle and Martin Pätzold and Erik A Petigura and Jorge Prieto-Arranz and Heike Rauer and Paul Robertson and Mark E. Rose and Arpita Roy and Paula Sarkis and Joshua E. Schlieder and Damien Ségransan and Stephen Shectman and Marek Skarka and Alexis M. S. Smith and Jeffrey C. Smith and Keivan Stassun and Johanna Teske and Joseph D. Twicken and Vincent Van Eylen and Sharon Wang and Lauren M. Weiss and Aurélien Wyttenbach},
journal= {arXiv preprint arXiv:2004.10095},
year = {2021}
}