Kepler-539: A young extrasolar system with two giant planets on wide orbits and in gravitational interaction

Mancini, L.; Lillo-Box, J.; Southworth, J.; Borsato, L.; Gandolfi, D.; Ciceri, S.; Barrado, D.; Brahm, R.; Th. Henning

Abstract

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.

Citation

Mancini, L., Lillo-Box, J., Southworth, J., Borsato, L., Gandolfi, D., Ciceri, S., …Th. Henning. (2016). Kepler-539: A young extrasolar system with two giant planets on wide orbits and in gravitational interaction. Astronomy & Astrophysics, 590, Article A112. https://doi.org/10.1051/0004-6361/201526357

• Journal Article Type: Article
• Acceptance Date: Apr 19, 2016
• Online Publication Date: May 25, 2016
• Publication Date: 2016-06
• Journal: Astronomy & Astrophysics
• Print ISSN: 0004-6361
• Publisher: EDP Sciences
• Peer Reviewed: Peer Reviewed
• Volume: 590
• Article Number: A112
• DOI: https://doi.org/10.1051/0004-6361/201526357
• Keywords: planetary systems, stars, fundamental parameters, individual, Kepler-539
• Publisher URL: http://dx.doi.org/10.1051/0004-6361/201526357