A false positive transit candidate for EPIC 211101996 from K2 and TESS data identified as background eclipsing binary Gaia DR3 66767847894609792

TL;DR

This study demonstrates that a transit signal initially attributed to a young star in the Pleiades was actually caused by a background eclipsing binary, highlighting the importance of detailed analysis to avoid false positives in exoplanet detection.

Contribution

The paper identifies a false positive transit signal as a background eclipsing binary, emphasizing the need for careful source analysis in exoplanet searches around young stars.

Findings

The initial transit signal was caused by a background eclipsing binary.

The contaminant is a grazing eclipsing binary with a 6-day period.

Proper analysis can prevent false positive exoplanet detections.

Abstract

Transiting planets around young stars are hard to find due to the enhanced stellar activity. Only a few transiting planets have been detected around stars younger than 100 Myr. We initially detected a transit-like signal in the K2 light curve of a very cool M dwarf star (EPIC 211101996) in the Pleiades open cluster, with an estimated age of about 100 Myr. Our detailed analysis of the per-pixel light curves, detrending with the W\={o}tan software and transit search with the Transit Least Squares algorithm showed that the source of the signal is a contaminant source (Gaia DR3 66767847894609792) 20" west of the target. The V-like shape of its phase-folded light curve and eclipse depth of ~15% suggest that it is a grazing eclipsing binary. The contaminant has hitherto been listed as a single star, which we now identify as an eclipsing stellar binary with a period of about 6 days.