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 } \leavevmode \nobreak M _ { \odot } and 1.657 ^ { +0.020 } _ { -0.004 } \leavevmode \nobreak R _ { \odot } , respectively .
The star appears to have recently left the main sequence , based on the inferred age , 9.4 ^ { +0.4 } _ { -1.3 } \leavevmode \nobreak \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 \leavevmode \nobreak 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 \leavevmode \nobreak 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 .