Kepler-77b: a very low albedo, Saturn-mass transiting planet around a metal-rich solar-like star⋆,⋆⋆,⋆⋆⋆,⋆⋆⋆⋆
Research and Scientific Support Department, European Space Agency (ESA/ESTEC),
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2 Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38205 La Laguna, Spain
3 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
4 Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
5 INAF−Osservatorio Astrofisico di Catania, Via S. Sofia, 78, 95123 Catania, Italy
6 Physics Department “E. Fermi”, University of Pisa, largo B. Pontecorvo 3, 56127 Pisa, Italy
7 Istituto Nazionale di Fisica Nucleare, largo B. Pontecorvo 3, 56127 Pisa, Italy
8 School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv Uni., 69978 Tel Aviv, Israel
9 Department of Physics, University of Oxford, Oxford, OX1 3RH, UK
10 Stellar Astrophysics Centre, Department of Physics and Astronomy, Århus Uni., Ny Munkegade 120, 8000 Århus C, Denmark
11 Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
12 KU Leuven, Centre for mathematical Plasma Astrophysics, Celestijnenlaan 200B, 3001 Leuven, Belgium
13 Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
14 Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
Accepted: 28 June 2013
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 at McDonald and FIES at 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 Mp = 0.430 ± 0.032 MJup, a radius of Rp = 0.960 ± 0.016 RJup, and a bulk density of ρp = 0.603 ± 0.055 g cm-3. It orbits a slowly rotating (Prot = 36 ± 6 days) G5 V star with M⋆ = 0.95 ± 0.04 M⊙, R⋆ = 0.99 ± 0.02 R⊙, Teff = 5520 ± 60 K, [M/H] = 0.20 ± 0.05 dex, that has an age of 7.5 ± 2.0 Gyr. The lack of detectable planetary occultation with a depth higher than ~10 ppm implies a planet geometric and Bond albedo of Ag ≤ 0.087 ± 0.008 and AB ≤ 0.058 ± 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 ~0.5 min, in accordance with the trend that close-in gas giant planets seem to belong to single-planet systems. The 106 transitsobserved 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.
Key words: planetary systems / stars: fundamental parameters / stars: individual: Kepler-77 / techniques: photometric / techniques: radial velocities / techniques: spectroscopic
Based on observations obtained with the 2.1-m Otto Struve telescope at McDonald Observatory, Texas, USA.
Based on observations obtained with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in time allocated by OPTICON and the Spanish Time Allocation Committee (CAT).
The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement number RG226604 (OPTICON).
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2013