The CARMENES search for exoplanets around M dwarfs. Two planets on opposite sides of the radius gap transiting the nearby M dwarf LTT 3780

Publication date: 
Main author: 
Nowak, G.
IAA authors: 
Rodríguez-López, C.;Aceituno, F. J.;Amado, P. J.;Bauer, F. F.
Nowak, G.;Luque, R.;Parviainen, H.;Pallé, E.;Molaverdikhani, K.;Béjar, V. J. S.;Lillo-Box, J.;Rodríguez-López, C.;Caballero, J. A.;Zechmeister, M.;Passegger, V. M.;Cifuentes, C.;Schweitzer, A.;Narita, N.;Cale, B.;Espinoza, N.;Murgas, F.;Hidalgo, D.;Zapatero Osorio, M. R.;Pozuelos, F. J.;Aceituno, F. J.;Amado, P. J.;Barkaoui, K.;Barrado, D.;Bauer, F. F.;Benkhaldoun, Z.;Caldwell, D. A.;Casasayas Barris, N.;Chaturvedi, P.;Chen, G.;Collins, K. A.;Collins, K. I.;Cortés-Contreras, M.;Crossfield, I. J. M.;de León, J. P.;Díez Alonso, E.;Dreizler, S.;El Mufti, M.;Esparza-Borges, E.;Essack, Z.;Fukui, A.;Gaidos, E.;Gillon, M.;Gonzales, E. J.;Guerra, P.;Hatzes, A.;Henning, Th.;Herrero, E.;Hesse, K.;Hirano, T.;Howell, S. B.;Jeffers, S. V.;Jehin, E.;Jenkins, J. M.;Kaminski, A.;Kemmer, J.;Kielkopf, J. F.;Kossakowski, D.;Kotani, T.;Kürster, M.;Lafarga, M.;Latham, D. W.;Law, N.;Lissauer, J. J.;Lodieu, N.;Madrigal-Aguado, A.;Mann, A. W.;Massey, B.;Matson, R. A.;Matthews, E.;Montañés-Rodríguez, P.;Montes, D.;Morales, J. C.;Mori, M.;Nagel, E.;Oshagh, M.;Pedraz, S.;Plavchan, P.;Pollacco, D.;Quirrenbach, A.;Reffert, S.;Reiners, A.;Ribas, I.;Ricker, G. R.;Rose, M. E.;Schlecker, M.;Schlieder, J. E.;Seager, S.;Stangret, M.;Stock, S.;Tamura, M.;Tanner, A.;Teske, J.;Trifonov, T.;Twicken, J. D.;Vanderspek, R.;Watanabe, D.;Wittrock, J.;Ziegler, C.;Zohrabi, F.
Astronomy and Astrophysics
Publication type: 
We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (d<SUB>⋆</SUB> ≈ 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<SUB>eff</SUB> = 3360 ± 51 K, a surface gravity of log g<SUB>⋆</SUB> = 4.81 ± 0.04 (cgs), and an iron abundance of [Fe/H] = 0.09 ± 0.16 dex, with an inferred mass of M<SUB>⋆</SUB> = 0.379 ± 0.016M<SUB>☉</SUB> and a radius of R<SUB>⋆</SUB> = 0.382 ± 0.012R<SUB>☉</SUB>. The ultra-short-period planet LTT 3780 b (P<SUB>b</SUB> = 0.77 d) with a radius of 1.35<SUB>-0.06</SUB><SUP>+0.06</SUP> R<SUB>⊕</SUB>, a mass of 2.34<SUP>-0.23</SUP><SUB>+0.24</SUB> M<SUB>⊕</SUB>, and a bulk density of 5.24<SUB>-0.81</SUB><SUP>+0.94</SUP> g cm<SUP>-3</SUP> 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<SUB>-0.10</SUB><SUP>+0.10</SUP> R<SUB>⊕</SUB>, mass of 6.29<SUB>-0.61</SUB><SUP>+0.63</SUP> M<SUB>⊕</SUB>, and mean density of 2.45<SUB>-0.37</SUB><SUP>+0.44</SUP> g cm<SUP>-3</SUP> 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).
ADS Bibcode: 
techniques: photometric;techniques: radial velocities;stars: individual: LTT 3780;stars: late-type;planets and satellites: detection;Astrophysics - Earth and Planetary Astrophysics;Astrophysics - Solar and Stellar Astrophysics