The K2-ESPRINT project. VI. K2-105 b, a hot Neptune around a metal-rich G-dwarf

Norio Narita, Teruyuki Hirano, Akihiko Fukui, Yasunori Hori, Fei Dai, Liang Yu, John Livingston, Tsuguru Ryu, Grzegorz Nowak, Masayuki Kuzuhara, Bun'ei Sato, Yoichi Takeda, Simon Albrecht, Tomoyuki Kudo, Nobuhiko Kusakabe, Enric Palle, Ignasi Ribas, Motohide Tamura, Vincent Van Eylen, Joshua N. Winn

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We report on the confirmation that the candidate transits observed for the star EPIC 211525389 are due to a short-period Neptune-sized planet. The host star, located in K2 campaign field 5, is a metal-rich ([Fe/H] = 0.26 ± 0.05) G-dwarf (Teff = 5430 ± 70 K and log g = 4.48 ± 0.09), based on observations with the High Dispersion Spectrograph (HDS) on the Subaru 8.2 m telescope. High spatial resolution AO imaging with HiCIAO on the Subaru telescope excludes faint companions near the host star, and the false positive probability of this target is found to be <10-6 using the open source vespa code. A joint analysis of transit light curves from K2 and additional ground-based multicolor transit photometry with MuSCAT on the Okayama 1.88 m telescope gives an orbital period of P = 8.266902 ± 0.000070 d and consistent transit depths of Rp/Rblack star ∼ 0.035 or (Rp/Rblack star)2 ∼ 0.0012. The transit depth corresponds to a planetary radius of Rp = 3.59-0.39+0.44 R, indicating that EPIC 211525389 b is a short-period Neptune-sized planet. Radial velocities of the host star, obtained with the Subaru HDS, lead to a 3 σ upper limit of 90 M (0.00027 M) on the mass of EPIC 211525389 b, confirming its planetary nature. We expect this planet, newly named K2-105 b, to be the subject of future studies to characterize its mass, atmosphere, and spin-orbit (mis)alignment, as well as investigate the possibility of additional planets in the system.

Original languageEnglish (US)
Article number29
JournalPublications of the Astronomical Society of Japan
Issue number2
StatePublished - Apr 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Planets and satellites: individual (K2-105 b = EPIC 211525389 b)
  • Stars: individual (TYC 807-1019-1 = EPIC 211525389)
  • Techniques: high angular resolution
  • Techniques: photometric
  • Techniques: radial velocities
  • Techniques: spectroscopic


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