TOI-6692b: An eccentric 130 day period giant planet with a single transit from TESS

TL;DR

This paper reports the discovery and detailed characterization of TOI-6692b, a highly eccentric giant planet with a 130-day orbit, confirmed through multiple radial velocity measurements and ground-based photometry, showcasing the potential of combined observational methods.

Contribution

It presents the first confirmed long-period giant planet from a single TESS transit, demonstrating effective follow-up strategies for such challenging detections.

Findings

TOI-6692b has an eccentricity of ~0.54 and a 130-day orbit.

The planet's mass and radius are securely measured, confirming its giant nature.

Follow-up observations successfully refined the orbital period despite initial uncertainties.

Abstract

We report the discovery and characterization of TOI-6692 b, an eccentric (e~0.54) Jupiter on a 130-day orbit. TOI-6692 b was first detected as a community TESS Object of Interest (cTOI) by the Visual Survey Group and the Planet Hunters group as a single transit candidate via TESS observation. The period was subsequently confirmed via radial velocity monitoring from the Planet Finder Spectrograph on the 6.5m Magellan telescope. Additional radial velocities were acquired with the CHIRON, FEROS, and CORALIE spectrographs. LCOGT ground-based photometric follow-up was conducted over 2 weeks to detect another transit and refine the period. Although we did not detect an ingress or egress of the 11.04 hr transit, we did detect a possible in-transit signal in the multi-night data and provide an updated ephemeris for future monitoring. TOI-6692 b is one of few planets with orbital periods longer than 100 days that have a secure mass, radius, and eccentricity detection. As with most giant planets at these orbital periods, the eccentricity of TOI-6692 b is lower than that expected of planets undergoing high-eccentricity tidal migration, but is more consistent with the expectations of planet-planet scattering outcomes. A long-term radial velocity trend was detected and further monitoring is warranted to determine the outer companion period. TOI-6692 b is also one of few TESS single transit targets that have its period eventually confirmed via follow-up photometric campaigns timed to capture transits despite the relatively large ephemeris uncertainties. Such efforts highlight the capabilities of night-to-night stability on ground-based photometric facilities today.