The Multiplanet System TOI-421

Summary, in English

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 Transiting Exoplanet Survey Satellite (TESS) space mission in Sectors 5 and 6. We performed ground-based follow-up observations - comprised of Las Cumbres Observatory Global Telescope transit photometry, NIRC2 adaptive optics imaging, and FIbre-fed Echellé Spectrograph, CORALIE, High Accuracy Radial velocity Planet Searcher, High Resolution chelle Spectrometer, and Planet Finder Spectrograph 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 five 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-421 b, has an orbital period of P b = 5.19672 ± 0.00049 days, a mass of M b = 7.17 ± 0.66 M ⊕, and a radius of R b = 2.68-0.18+0.19 R ⊕, whereas the outer warm Neptune, TOI-421 c, has a period of P c = 16.06819 ± 0.00035 days, a mass of M c = 16.42-1.04+1.06 M ⊕, a radius of R c = 5.09-0.15+0.16 R ⊕, and a density of ρ c = 0.685-0.072+0.080 g cm-3. With its characteristics, the outer planet (ρ c = 0.685-0.072+0.080 g cm-3) is placed in the intriguing class of the super-puffy mini-Neptunes. TOI-421 b and TOI-421 c are found to be well-suited for atmospheric characterization. Our atmospheric simulations predict significant Lyα transit absorption, due to strong hydrogen escape in both planets, as well as the presence of detectable CH4 in the atmosphere of TOI-421 c if equilibrium chemistry is assumed.

• Author: Ilaria Carleo; Davide Gandolfi; Oscar Barragán; John H. Livingston; Carina M. Persson; Kristine W.F. Lam; Aline Vidotto; Michael B. Lund; Carolina Villarreal D'angelo; Karen A. Collins; Luca Fossati; Andrew W. Howard; Daria Kubyshkina; Rafael Brahm; Antonija Oklopčić; Paul Molli re; Seth Redfield; Luisa Maria Serrano; Fei Dai; Malcolm Fridlund; Francesco Borsa; Judith Korth; Massimiliano Esposito; Matías R. Díaz; Louise Dyregaard Nielsen; Coel Hellier; Savita Mathur; Hans J. Deeg; Artie P. Hatzes; Serena Benatti; Florian Rodler; Javier Alarcon; Lorenzo Spina; Angela R.G. Santos; Iskra Georgieva; Rafael A. García; Lucía González-Cuesta; George R. Ricker; Roland Vanderspek; David W. Latham; Sara Seager; Joshua N. Winn; Jon M. Jenkins; Simon Albrecht; Natalie M. Batalha; Corey Beard; Patricia T. Boyd; Fran ois Bouchy; Jennifer A. Burt; R. Paul Butler; Juan Cabrera; Ashley Chontos; David R. Ciardi; William D. Cochran; Kevin I. Collins; Jeffrey D. Crane; Ian Crossfield; Szilard Csizmadia; Diana Dragomir; Courtney Dressing; Philipp Eigmüller; Michael Endl; Anders Erikson; Nestor Espinoza; Michael Fausnaugh; Fabo Feng; Erin Flowers; Benjamin Fulton; Erica J. Gonzales; Nolan Grieves; Sascha Grziwa; Eike W. Guenther; Natalia M. Guerrero; Thomas Henning; Diego Hidalgo; Teruyuki Hirano; Maria Hjorth; Daniel Huber; Howard Isaacson; Matias Jones; Andrés Jordán; Petr Kabáth; Stephen R. Kane; Emil Knudstrup; Jack Lubin; Rafael Luque; Ismael Mireles; Norio Narita; David Nespral; Prajwal Niraula; Grzegorz Nowak; Enric Palle; Martin Patzold; Erik A. Petigura; Jorge Prieto-Arranz; Heike Rauer; Paul Robertson; Mark E. Rose; Arpita Roy; Paula Sarkis; Joshua E. Schlieder; Damien Ségransan; Stephen Shectman; Marek Skarka; Alexis M.S. Smith; Jeffrey C. Smith; Keivan Stassun; Johanna Teske; Joseph D. Twicken; Vincent Van Eylen; Sharon Wang; Lauren M. Weiss; Aurélien Wyttenbach
• Publishing year: 2020-09
• Language: English
• Publication/Series: Astronomical Journal
• Volume: 160
• Issue: 3
• Links: http://dx.doi.org/10.3847/1538-3881/aba124
• Document type: Journal article
• Publisher: IOP Publishing
• Status: Published
• ISBN/ISSN/Other: ISSN: 0004-6256