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arXiv · 2007.07939

K2-280b -- a low density warm sub-Saturn around a mildly evolved star

Grzegorz Nowak·Enric Palle·Davide Gandolfi·Hans J. Deeg·Teruyuki Hirano·Oscar Barragán·Masayuki Kuzuhara·Fei Dai·Rafael Luque·Carina M. Persson·Malcolm Fridlund·Marshall C. Johnson·Judith Korth·John H. Livingston·Sascha Grziwa·Savita Mathur·Artie P. Hatzes·Jorge Prieto-Arranz·David Nespral·Diego Hidalgo·Maria Hjorth·Simon Albrecht·Vincent Van Eylen·Kristine W. F. Lam·William D. Cochran·Massimiliano Esposito·Szilárd Csizmadia·Eike W. Guenther·Petr Kabath·Pere Blay·Rafael Brahm·Andrés Jordán·Néstor Espinoza·Felipe Rojas·Núria Casasayas Barris·Florian Rodler·Roi Alonso Sobrino·Juan Cabrera·Ilaria Carleo·Alexander Chaushev·Jerome de Leon·Philipp Eigmüller·Michael Endl·Anders Erikson·Akihiko Fukui·Iskra Georgieva·Lucía González-Cuesta·Emil Knudstrup·Mikkel N. Lund·Pilar Montañes Rodríguez·Felipe Murgas·Norio Narita·Prajwal Niraula·Martin Pätzold·Heike Rauer·Seth Redfield·Ignasi Ribas·Marek Skarka·Alexis M. S. Smith·Jano Subjak
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Abstract

We present an independent discovery and detailed characterisation of K2-280b, a transiting low density warm sub-Saturn in a 19.9-day moderately eccentric orbit (e = 0.35_{-0.04}^{+0.05}) from K2 campaign 7. A joint analysis of high precision HARPS, HARPS-N, and FIES radial velocity measurements and K2 photometric data indicates that K2-280b has a radius of R_b = 7.50 +/- 0.44 R_Earth and a mass of M_b = 37.1 +/- 5.6 M_Earth, yielding a mean density of 0.48_{-0.10}^{+0.13} g/cm^3. The host star is a mildly evolved G7 star with an effective temperature of T_{eff} = 5500 +/- 100 K, a surface gravity of log(g) = 4.21 +/- 0.05 (cgs), and an iron abundance of [Fe/H] = 0.33 +/- 0.08 dex, and with an inferred mass of M_star = 1.03 +/- 0.03 M_sun and a radius of R_star = 1.28 +/- 0.07 R_sun. We discuss the importance of K2-280b for testing formation scenarios of sub-Saturn planets and the current sample of this intriguing group of planets that are absent in the Solar System.

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Grzegorz Nowak, Enric Palle, Davide Gandolfi, Hans J. Deeg, Teruyuki Hirano, Oscar Barragán, Masayuki Kuzuhara, Fei Dai, Rafael Luque, Carina M. Persson, Malcolm Fridlund, Marshall C. Johnson, Judith Korth, John H. Livingston, Sascha Grziwa, Savita Mathur, Artie P. Hatzes, Jorge Prieto-Arranz, David Nespral, Diego Hidalgo, Maria Hjorth, Simon Albrecht, Vincent Van Eylen, Kristine W. F. Lam, William D. Cochran, Massimiliano Esposito, Szilárd Csizmadia, Eike W. Guenther, Petr Kabath, Pere Blay, Rafael Brahm, Andrés Jordán, Néstor Espinoza, Felipe Rojas, Núria Casasayas Barris, Florian Rodler, Roi Alonso Sobrino, Juan Cabrera, Ilaria Carleo, Alexander Chaushev, Jerome de Leon, Philipp Eigmüller, Michael Endl, Anders Erikson, Akihiko Fukui, Iskra Georgieva, Lucía González-Cuesta, Emil Knudstrup, Mikkel N. Lund, Pilar Montañes Rodríguez, Felipe Murgas, Norio Narita, Prajwal Niraula, Martin Pätzold, Heike Rauer, Seth Redfield, Ignasi Ribas, Marek Skarka, Alexis M. S. Smith, Jano Subjak. 2020-07-15. K2-280b -- a low density warm sub-Saturn around a mildly evolved star. https://doi.org/10.1093/mnras%2Fstaa2077

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