* Astronomy

Title: KOI-127b: a very low-albedo, Saturn-mass transiting planet around a metal rich solar-like star
Authors: D. Gandolfi, H. Parviainen, M. Fridlund, A. P. Hatzes, H. J. Deeg, A. Frasca, A. F. Lanza, P. G. Prada Moroni, E. Tognelli, A. McQuillan, S. Aigrain, R. Alonso, V. Antoci, J. Cabrera, L. Carone, Sz. Csizmadia, A. A. Djupvik, E. W. Günther, J. Jessen-Hansen, A. Ofir, J. Telting

We report the discovery of KOI-127b, 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 Markov chain Monte Carlo simulation. KOI-127b is a moderately inflated planet with a mass of Mp=0.430±0.032 Jupiter masses, radius of Rp=0.960±0.016 Jupiter radii, and bulk density of 0.603±0.055 g/cm^3. It orbits a slowly rotating (P=36±6 days) G5V star with M*=0.95±0.04 solar masses, R*=0.99±0.02 solar radii, Teff=5520±60 K, [M/H]=0.20±0.05, and an age of 7.5±2.0 Gyr. The lack of detectable planetary occultation with a depth larger than about 10 ppm, implies a planet's geometric and Bond albedo of Ag<0.087±0.008 and Ab<0.058±0.006, respectively, placing KOI-127b among the gas-giant planets with the lowest albedo known so far. We found neither additional planetary transit signals, nor transit timing variations (TTVs) at a level of about 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.

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