Validation and atmospheric exploration of the sub-Neptune TOI-2136b around a nearby M3 dwarf

Publication date: 
Main author: 
Kawauchi, K.
IAA authors: 
Luque, R.
Kawauchi, K.;Murgas, F.;Palle, E.;Narita, N.;Fukui, A.;Hirano, T.;Parviainen, H.;Ishikawa, H. T.;Watanabe, N.;Esparaza-Borges, E.;Kuzuhara, M.;Orell-Miquel, J.;Krishnamurthy, V.;Mori, M.;Kagetani, T.;Zou, Y.;Isogai, K.;Livingston, J. H.;Howell, S. B.;Crouzet, N.;de Leon, J. P.;Kimura, T.;Kodama, T.;Korth, J.;Kurita, S.;Laza-Ramos, A.;Luque, R.;Madrigal-Aguado, A.;Miyakawa, K.;Morello, G.;Nishiumi, T.;Rodríguez, G. E. F.;Sánchez-Benavente, M.;Stangret, M.;Teng, H.;Terada, Y.;Gnilka, C. L.;Guerrero, N.;Harakawa, H.;Hodapp, K.;Hori, Y.;Ikoma, M.;Jacobson, S.;Konishi, M.;Kotani, T.;Kudo, T.;Kurokowa, T.;Kusakabe, N.;Nishikawa, J.;Omiya, M.;Serizawa, T.;Tamura, M.;Ueda, A.;Vievard, S.
Astronomy and Astrophysics
Publication type: 
Context. The NASA space telescope TESS is currently in the extended mission of its all-sky search for new transiting planets. Of the thousands of candidates that TESS is expected to deliver, transiting planets orbiting nearby M dwarfs are particularly interesting targets since they provide a great opportunity to characterize their atmospheres by transmission spectroscopy. <BR /> Aims: We aim to validate and characterize the new sub-Neptune-sized planet candidate TOI-2136.01 orbiting a nearby M dwarf (d = 33.36 ± 0.02pc, T<SUB>eff</SUB> = 3373 ± 108 K) with an orbital period of 7.852 days. <BR /> Methods: We use TESS data, ground-based multicolor photometry, and radial velocity measurements with the InfraRed Doppler (IRD) instrument on the Subaru Telescope to validate the planetary nature of TOI-2136.01, and estimate the stellar and planetary parameters. We also conduct high-resolution transmission spectroscopy to search for helium in its atmosphere. <BR /> Results: We confirm that TOI-2136.01 (now named TOI-2136b) is a bona fide planet with a planetary radius of R<SUB>p</SUB> = 2.20 ± 0.07R<SUB>⊕</SUB> and a mass of M<SUB>p</SUB> = 4.7<SUB>−2.6</SUB><SUP>+3.1</SUP> M<SUB>⊕</SUB>. We also search for helium 10830 Å absorption lines and place an upper limit on the equivalent width of &lt;7.8 mÅ and on the absorption signal of &lt;1.44% with 95% confidence. <BR /> Conclusions: TOI-2136b is a sub-Neptune transiting a nearby and bright star (J = 10.8 mag), and is a potentially hycean planet, which is a new class of habitable planets with large oceans under a H<SUB>2</SUB>-rich atmosphere, making it an excellent target for atmospheric studies to understand the formation, evolution, and habitability of the small planets.
ADS Bibcode: 
planets and satellites: individual: TOI-2136b;planets and satellites: detection;planets and satellites: atmospheres;techniques: photometric;techniques: radial velocities;Astrophysics - Earth and Planetary Astrophysics