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K2 Targets Observed with SPHERE/VLT: An M4-7 Dwarf Companion Resolved around EPIC 206011496

R. Ligi, O. Demangeon, S. C. C. Barros, D. Mesa, M. Bonavita, A. Vigan, M. Bonnefoy, R. Gratton, M. Deleuil

Abstract
The quest to discover exoplanets is one of the most important missions in astrophysics, and is widely performed using the transit method, which allows for the detection of exoplanets down to the size of Mercury. However, to confirm these detections, additional vetting is mandatory. We selected six K2 targets from campaigns #1 to #8 that show transit light curves corresponding to Earth-sized to Neptune-sized exoplanets. We aim to discard some scenarios that could mimic an exoplanetary transit, leading to a misinterpretation of the data. We performed direct imaging observations using the SPHERE/VLT instrument to probe the close environment of these stars. For five of the K2 targets, we report no detection and we give the detection limits. For EPIC 206011496, we detect a 0.38±0.06 M companion at a separation of 977.12±0.73 mas (140.19±0.11 au). The spectral analysis corresponds to an M4-7 star, and the analysis of the proper motion shows that it is bounded to the primary star. EPIC 206011496 also hosts an Earth-like planetary candidate. If it transits the primary star, its radius is consistent with that of a super-Earth. However, if it transits the companion star, it falls into the mini-Neptune regime.

Keywords
binaries: general; binaries: visual; planetary systems; stars: individual (EPIC 206011496) ; techniques: high angular resolution

Notes
- Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 98.C-0779(A) and 99.C-0.276(A).
- This work is based on data products produced at the SPHERE Data Center hosted at OSUG/IPAG, Grenoble.

The Astronomical Journal
Volume 156, Number 4
2018 October

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia