Volume 590, June 2016
|Number of page(s)||12|
|Section||Planets and planetary systems|
|Published online||25 May 2016|
Kepler-539: A young extrasolar system with two giant planets on wide orbits and in gravitational interaction⋆
1 Max-Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
2 INAF–Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
3 Depto. de Astrofísica, Centro de Astrobiologìa (CSIC-INTA), ESAC campus, 28691 Villanueva de la Cañada, Spain
4 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
5 Astrophysics Group, Keele University, Keele ST5 5BG, UK
6 Dip. di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
7 Dip. di Fisica, Università di Torino, via P. Giuria 1, 10125 Torino, Italy
8 Landessternwarte Königstuhl, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
9 Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
10 Millennium Institute of Astrophysics, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
Received: 19 April 2015
Accepted: 19 April 2016
We confirm the planetary nature of Kepler-539 b (aka Kepler object of interest K00372.01), a giant transiting exoplanet orbiting a solar-analogue G2 V star. The mass of Kepler-539 b was accurately derived thanks to a series of precise radial velocity measurements obtained with the CAFE spectrograph mounted on the CAHA 2.2-m telescope. A simultaneous fit of the radial-velocity data and Kepler photometry revealed that Kepler-539 b is a dense Jupiter-like planet with a mass of Mp = 0.97 ± 0.29 MJup and a radius of Rp = 0.747 ± 0.018 RJup, making a complete circular revolution around its parent star in 125.6 days. The semi-major axis of the orbit is roughly 0.5 au, implying that the planet is at ≈0.45 au from the habitable zone. By analysing the mid-transit times of the 12 transit events of Kepler-539 b recorded by the Kepler spacecraft, we found a clear modulated transit time variation (TTV), which is attributable to the presence of a planet c in a wider orbit. The few timings available do not allow us to precisely estimate the properties of Kepler-539 c and our analysis suggests that it has a mass between 1.2 and 3.6 MJup, revolving on a very eccentric orbit (0.4 <e ≤ 0.6) with a period larger than 1000 days. The high eccentricity of planet c is the probable cause of the TTV modulation of planet b. The analysis of the CAFE spectra revealed a relatively high photospheric lithium content, A(Li) = 2.48 ± 0.12 dex, which, together with both a gyrochronological and isochronal analysis, suggests that the parent star is relatively young.
Key words: planetary systems / stars: fundamental parameters / stars: individual: Kepler-539
RV/BVS measurements are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A112
© ESO, 2016
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