TOI-6692 b: An Eccentric 130 Day Period Giant Planet with a Single Transit from TESS

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 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 6.5 m 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 multinight data and provide an updated ephemeris for future monitoring. TOI-6692 b is one of the 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 the few TESS single transit targets to have its periods 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.