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. Nowak, E. 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
HD 89345: a bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2
See arXiv version
Submitted to MNRAS on 23 February 2018, accepted for publication, 4 May 2018
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 one-minute time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding the mass and radius to be \(1.12^{+0.04}_{-0.01}~M_\odot\) and \(1.657^{+0.020}_{-0.004}~R_\odot\), respectively. The star appears to have recently left the main sequence, based on the inferred age, \(9.4^{+0.4}_{-1.3}~\mathrm{Gyr}\), and the non-detection of mixed modes. The star hosts a “warm Saturn” (\(P = 11.8\)~days, \(R_p = 6.86 \pm 0.14~R_\oplus\)). Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of \(35.7 \pm 3.3~M_\oplus\). The data also show that the planet’s orbit is eccentric (\(e\approx 0.2\)). 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 conform to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.
