The CARMENES search for exoplanets around M dwarfs
G. Nowak, R. Luque, H. Parviainen, Ε. Πάλλη, Karan Molaverdikhani, V. J. S. Béjar, J. Lillo-Box, C. López, J. A. Caballero, M. Zechmeister, V. M. Passegger, C. Cifuentes, A. Schweitzer, Norio Narita, Bryson Cale, Néstor Espinoza, F. Murgas, D. Hidalgo, M. R. Zapatero Osorio, F. J. Pozuelos, F. J. Aceituno, P. J. Amado, Khalid Barkaoui, D. Barrado, F. F. Bauer, Z. Benkhaldoun, Douglas A. Caldwell, N. Casasayas Barris, P. Chaturvedi, G. Chen, Karen A. Collins, Kevin I. Collins, M. Cortés‐Contreras, Ian J. M. Crossfield, Jerome de Leon, E. Díez-Alonso, S. Dreizler, Mohammed El Mufti, E. Esparza-Borges, Zahra Essack, Akihiko Fukui, Eric Gaidos, M. Gillon, Erica J. Gonzales, P. Guerra, A. P. Hatzes, Th. Henning, E. Herrero, Katharine Hesse, Teruyuki Hirano, Steve B. Howell, S. V. Jeffers, E. Jehin, Jon M. Jenkins, A. Kaminski, J. Kemmer, John F. Kielkopf, D. Kossakowski, Takayuki Kotani, M. Kürster, M. Lafarga, David W. Latham, Nicholas M. Law, Jack J. Lissauer, N. Lodieu, A. Madrigal-Aguado, Andrew W. Mann, Bob Massey, Rachel A. Matson, Elisabeth C. Matthews, P. Montañés‐Rodríguez, D. Montes, J. C. Morales, M. Mori, E. Nagel, M. Oshagh, S. Pedraz, Peter Plavchan, D. Pollacco, A. Quirrenbach, S. Reffert, A. Reiners, I. Ribas, G. Ricker, Mark E. Rose, Martin Schlecker, Joshua E. Schlieder, Sara Seager, M. Stangret, S. Stock, Motohide Tamura, Angelle Tanner, Johanna Teske, Trifon Trifonov, Joseph D. Twicken, R. Vanderspek, David Watanabe, Justin M. Wittrock, Carl Ziegler, Farzaneh Zohrabi
Abstract
We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby ( d ⋆ ≈ 22 pc), bright ( J ≈ 9 mag) M3.5 dwarf LTT 3780 (TOI–732). We confirm both planets and their association with LTT 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the CARMENES spectrograph. Precise stellar parameters determined from CARMENES high-resolution spectra confirm that LTT 3780 is a mid-M dwarf with an effective temperature of T eff = 3360 ± 51 K, a surface gravity of log g ⋆ = 4.81 ± 0.04 (cgs), and an iron abundance of [Fe/H] = 0.09 ± 0.16 dex, with an inferred mass of M ⋆ = 0.379 ± 0.016 M ⊙ and a radius of R ⋆ = 0.382 ± 0.012 R ⊙ . The ultra-short-period planet LTT 3780 b ( P b = 0.77 d) with a radius of 1.35 −0.06 +0.06 R ⊕ , a mass of 2.34 −0.23 +0.24 M ⊕ , and a bulk density of 5.24 −0.81 +0.94 g cm −3 joins the population of Earth-size planets with rocky, terrestrial composition. The outer planet, LTT 3780 c, with an orbital period of 12.25 d, radius of 2.42 −0.10 +0.10 R ⊕ , mass of 6.29 −0.61 +0.63 M ⊕ , and mean density of 2.45 −0.37 +0.44 g cm −3 belongs to the population of dense sub-Neptunes. With the two planets located on opposite sides of the radius gap, this planetary system is anexcellent target for testing planetary formation, evolution, and atmospheric models. In particular, LTT 3780 c is an ideal object for atmospheric studies with the James Webb Space Telescope (JWST).