TOI-222: a single-transit TESS candidate revealed to be a 34-day eclipsing binary with CORALIE, EulerCam and NGTS

TL;DR

This study demonstrates how combining radial velocity data with ground-based photometry can effectively confirm and characterize long-period eclipsing binaries initially identified as single-transit events by TESS.

Contribution

The paper introduces a method to determine the period and nature of a long-period binary from a single TESS transit using follow-up observations.

Findings

The companion is a low-mass star with 0.23 solar masses.

The orbital period is confirmed as 33.9 days.

Ground-based follow-up enables detailed characterization.

Abstract

We report the period, eccentricity, and mass determination for the TESS single-transit event candidate TOI-222, which displayed a single 3000 ppm transit in the TESS two-minute cadence data from Sector 2. We determine the orbital period via radial velocity measurements (P=33.9,days), which allowed for ground-based photometric detection of two subsequent transits. Our data show that the companion to TOI-222 is a low mass star, with a radius of $0.18_{-0.10}^{+0.39}$ Rsun and a mass of $0.23\pm0.01$ Msun. This discovery showcases the ability to efficiently discover long-period systems from TESS single transit events using a combination of radial velocity monitoring coupled with high precision ground-based photometry.