CoRoT LRa02_E2_0121: Neptune-size planet candidate turns into a hierarchical triple system with a giant primary

TL;DR

This study reclassifies CoRoT LRa02_E2_0121 from a Neptune-sized planet candidate to a hierarchical triple star system with a primary star and an eclipsing binary, based on detailed spectroscopic and photometric analysis.

Contribution

It demonstrates the use of combined spectroscopic and photometric methods to identify complex hierarchical stellar systems previously mistaken for exoplanet candidates.

Findings

Reclassified the system as a hierarchical triple with an evolved G-type primary.

Detected a secondary eclipse indicating an eclipsing binary within the system.

Showed the difficulty of identifying such systems without detailed follow-up observations.

Abstract

This paper presents the case of CoRoT LRa02_E2_0121, which was initially classified as a Neptune-size transiting-planet candidate on a relatively wide orbit of 36.3 days. Follow-up observations were performed with UVES, Sandiford, SOPHIE and HARPS. These observations revealed a faint companion in the spectra. To find the true nature of the system we derived the radial velocities of the faint companion using TODMOR - a two-dimensional correlation technique, applied to the SOPHIE spectra. Modeling the lightcurve with EBAS we discovered a secondary eclipse with a depth of ~0.07%, indicating a diluted eclipsing binary. Combined MCMC modeling of the lightcurve and the radial velocities suggested that CoRoT LRa02_E2_0121 is a hierarchical triple system with an evolved G-type primary and an A-type:F-type grazing eclipsing binary. Such triple systems are difficult to discover.