It takes two planets in resonance to tango around K2-146

25 Jul 2019  ·  Kristine W. F. Lam, Judith Korth, Kento Masuda, Szilárd Csizmadia, Philipp Eigmüller, Guðmundur Kári Stefánsson, Michael Endl, Simon Albrecht, Rafael Luque, John H. Livingston, Teruyuki Hirano, Roi Alonso Sobrino, Oscar Barragán, Juan Cabrera, Ilaria Carleo, Alexander Chaushev, William D. Cochran, Fei Dai, Jerome de Leon, Hans J. Deeg, Anders Erikson, Massimiliano Esposito, Malcolm Fridlund, Akihiko Fukui, Davide Gandolfi, Iskra Georgieva, Lucá Gonzalez Cuesta, Sascha Grziwa, Eike W. Guenther, Artie P. Hatzes, Diego Hidalgo, Maria Hjorth, Petr Kabath, Emil Knudstrup, Mikkel N. Lund, Suvrath Mahadevan, Savita Mathur, Pilar Montañes Rodríguez, Felipe Murgas, Norio Narita, David Nespral, Prajwal Niraula, Enric Palle, Martin Pätzold, Carina M. Persson, Jorge Prieto-Arranz, Heike Rauer, Seth Redfield, Ignasi Ribas, Paul Robertson, Marek Skarka, Alexis M. S. Smith, Jan Subjak, Vincent Van Eylen ·

K2-146 is a cool, 0.358 M_sun dwarf that was found to host a mini-Neptune with a 2.67-days period. The planet exhibited strong transit timing variations (TTVs) of greater than 30 minutes, indicative of the presence of a further object in the system... Here we report the discovery of the previously undetected outer planet, K2-146 c, in the system using additional photometric data. K2-146 c was found to have a grazing transit geometry and a 3.97-day period. The outer planet was only significantly detected in the latter K2 campaigns presumably because of precession of its orbital plane. The TTVs of K2-146 b and c were measured using observations spanning a baseline of almost 1200 days. We found strong anti-correlation in the TTVs, suggesting the two planets are gravitationally interacting. Our TTV and transit model analyses revealed that K2-146 b has a radius of 2.25 $\pm$ 0.10 \R_earth and a mass of 5.6 $\pm$ 0.7 M_earth, whereas K2-146 c has a radius of $2.59_{-0.39}^{+1.81}$ R_earth and a mass of 7.1 $\pm$ 0.9 M_earth. The inner and outer planets likely have moderate eccentricities of $e = 0.14 \pm 0.07$ and $0.16 \pm 0.07$, respectively. Long-term numerical integrations of the two-planet orbital solution show that it can be dynamically stable for at least 2 Myr. The evaluation of the resonance angles of the planet pair indicates that K2-146 b and c are likely trapped in a 3:2 mean motion resonance. The orbital architecture of the system points to a possible convergent migration origin. read more

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Earth and Planetary Astrophysics