HD 89345: a bright oscillating star hosting a transiting warm Saturn-sized planet observed by K2
Deeg, H.; Fridlund, M.; García, R. A.; Chaplin, W. J.; Barragán, O.; Dai, F.; Gandolfi, D.; Hirano, T.; Korth, J.; Prieto-Arranz, J.; Nespral, D.; Hjorth, M.; Grziwa, S.; Albrecht, S.; Hatzes, A. P.; Smith, A. M. S.; Narita, N.; Cochran, W. D.; Palle, E.; Persson, C. M.; Van Eylen, V.; Nowak, G.; Winn, J. N.; Lund, M. N.; Pérez Hernández, F.; Mathis, S.; Rodler, F.; Mathur, S.; Hidalgo, D.; Silva Aguirre, V.; Justesen, A. B.; Trifonov, T.; Endl, M.; Csizmadia, S.; Guenther, E.; Livingston, J.; Beck, P. G.; Regulo, C.; Patzold, M.; Everett, M. E.; Heeren, P.; Bugnet, L.; Montañes Rodriguez, P.
Netherlands, United States, Spain, Italy, Denmark, Sweden, France, Germany, Japan, United Kingdom, Chile
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 the mass and radius to be 1.12^{+0.04}_{-0.01} M_⊙ and 1.657^{+0.020}_{-0.004} R_⊙, respectively. The star appears to have recently left the main sequence, based on the inferred age, 9.4^{+0.4}_{-1.3} 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.