HD 89345: A bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2

V. Van Eylen, F. Dai, S. Mathur, D. Gandolfi, S. Albrecht, M. Fridlund, R. A. García, E. Guenther, M. Hjorth, A. B. Justesen, J. Livingston, M. N. Lund, F. Pérez Hernández, J. Prieto-Arranz, C. Regulo, L. Bugnet, M. E. Everett, T. Hirano, D. Nespral, G. NowakE. Palle, V. Silva Aguirre, T. Trifonov, J. N. Winn, O. Barragán, P. G. Beck, W. J. Chaplin, W. D. Cochran, S. Csizmadia, H. Deeg, M. Endl, P. Heeren, S. Grziwa, A. P. Hatzes, D. Hidalgo, J. Korth, S. Mathis, P. Montañes Rodriguez, N. Narita, M. Patzold, C. M. Persson, F. Rodler, A. M.S. Smith

Research output: Contribution to journalArticle

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Abstract

We report the discovery and characterization of HD 89345b (K2-234b; EPIC 248777106b), a Saturn-sized planet orbiting a slightly evolved star. HD 89345 is a bright star (V = 9.3 mag) observed by the K2 mission with 1 min time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding themass and radius to be 1.12-0.01 +0.04 M and 1.657 -0.004 +0.020 R, respectively. The star appears to have recently left the main sequence, based on the inferred age, 9.4-1.3 +0.4 Gyr, and the non-detection of mixed modes. The star hosts a 'warm Saturn' (P = 11.8 d, Rp = 6.86 ± 0.14 R). Radial-velocity follow-up observations performed with the FIbre-fed Echelle Spectrograph, HARPS, and HARPS-N spectrographs show that the planet has a mass of 35.7 ± 3.3 M. The data also show that the planet's orbit is eccentric (e≈0.2). An investigation of the rotational splitting of the oscillation frequencies of the star yields no conclusive evidence on the stellar inclination angle. We further obtained Rossiter-McLaughlin observations, which result in a broad posterior of the stellar obliquity. The planet seems to confirm to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.

Original languageEnglish (US)
Pages (from-to)4866-4880
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Volume478
Issue number4
DOIs
StatePublished - Aug 21 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Asteroseismology
  • Planets and satellites: composition
  • Planets and satellites: formation
  • Planets and satellites: fundamental parameters

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    Van Eylen, V., Dai, F., Mathur, S., Gandolfi, D., Albrecht, S., Fridlund, M., García, R. A., Guenther, E., Hjorth, M., Justesen, A. B., Livingston, J., Lund, M. N., Pérez Hernández, F., Prieto-Arranz, J., Regulo, C., Bugnet, L., Everett, M. E., Hirano, T., Nespral, D., ... Smith, A. M. S. (2018). HD 89345: A bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2. Monthly Notices of the Royal Astronomical Society, 478(4), 4866-4880. https://doi.org/10.1093/mnras/sty1390