K2-280 b-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 HidalgoMaria 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

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We present an independent discovery and detailed characterization of K2-280 b, a transiting low density warm sub-Saturn in a 19.9-d 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 K2-280 b has a radius of Rb = 7.50 ± 0.44 R⊕ and a mass of Mb = 37.1 ± 5.6 M⊕, yielding a mean density of ρb = 0.48 -0.10+0.13 g cm-3. The host star is a mildly evolved G7 star with an effective temperature of Teff = 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∗ = 1.03 ± 0.03 M⊙ and a radius of R∗ = 1.28 ± 0.07 R⊙. We discuss the importance of K2-280 b 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.

Original languageEnglish
Pages (from-to)4423-4435
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - 1 Oct 2020
Externally publishedYes


  • K2-280)
  • planets and satellites: detection
  • stars: individual: (EPIC 216494238
  • techniques: photometric
  • techniques: radial velocities
  • techniques: spectroscopic


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