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

TL;DR

This study used SPHERE/VLT imaging to investigate K2 exoplanet candidates, discovering a bound M4-7 dwarf companion to EPIC 206011496 and analyzing the implications for the planetary candidate’s nature.

Contribution

First direct imaging detection of a bound M4-7 dwarf companion around an exoplanet candidate host star, clarifying the system's architecture.

Findings

Detected a bound M4-7 dwarf companion at ~140 au from EPIC 206011496.

No additional companions detected around other K2 targets within detection limits.

The planetary candidate could be a super-Earth or mini-Neptune depending on the transiting star.

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 $\pm$ 0.06 $M_{\odot}$ companion at a separation of 977.12 $\pm$ 0.73 mas (140.19 $\pm$ 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.