We report the discovery of Kepler-77b ( alias KOI-127.01 ) , a Saturn-mass transiting planet in a 3.6-day orbit around a metal-rich solar-like star .
We combined the publicly available Kepler photometry ( quarters 1–13 ) with high-resolution spectroscopy from the Sandiford @ McDonald and FIES @ NOT spectrographs .
We derived the system parameters via a simultaneous joint fit to the photometric and radial velocity measurements .
Our analysis is based on the Bayesian approach and is carried out by sampling the parameter posterior distributions using a Markov chain Monte Carlo simulation .
Kepler-77b is a moderately inflated planet with a mass of M _ { \mathrm { p } } = 0.430 \pm 0.032 \mathrm { M } _ { \mathrm { Jup } } , a radius of R _ { \mathrm { p } } = 0.960 \pm 0.016 \mathrm { R } _ { \mathrm { Jup } } , and a bulk density of \rho _ { \mathrm { p } } = 0.603 \pm 0.055 g cm ^ { -3 } .
It orbits a slowly rotating ( P _ { \mathrm { rot } } = 36 \pm 6 days ) G5 V star with M _ { \star } = 0.95 \pm 0.04 M _ { \odot } , R _ { \star } = 0.99 \pm 0.02 R _ { \odot } , T _ { \mathrm { eff } } = 5520 \pm 60 K , [ M/H ] = 0.20 \pm 0.05 dex , that has an age of 7.5 \pm 2.0 Gyr .
The lack of detectable planetary occultation with a depth higher than \sim 10 ppm implies a planet geometric and Bond albedo of A _ { \mathrm { g } } \leq 0.087 \pm 0.008 and A _ { \mathrm { B } } \leq 0.058 \pm 0.006 , respectively , placing Kepler-77b among the gas-giant planets with the lowest albedo known so far .
We found neither additional planetary transit signals nor transit-timing variations at a level of \sim 0.5 minutes , in accordance with the trend that close-in gas giant planets seem to belong to single-planet systems .
The 106 transits observed in short-cadence mode by Kepler for nearly 1.2 years show no detectable signatures of the planet ’ s passage in front of starspots .
We explored the implications of the absence of detectable spot-crossing events for the inclination of the stellar spin-axis , the sky-projected spin-orbit obliquity , and the latitude of magnetically active regions .