TIC65910228 b: A single-transit discovery of a massive long-period warm Jupiter with TESS

Context. Warm Jupiters are excellent case studies for investigating giant planet internal structures and formation theories. However, the sample of long-period transiting giants today is not yet large enough to attain a better understanding of this population. Aims. Starting from a single transit found in the Transiting Exoplanet Survey Satellite (TESS) data, we confirmed the planetary nature of the signal and measured its orbital parameters, mass, and radius. We set this system in the context of long-period giant transiting planets and analyzed its viability for sustaining atmospheric or dynamical follow-ups. Methods. We carried out a spectroscopic follow-up using FEROS and PLATOSpec to obtain precise radial velocities. We added a photometric follow-up with HATPI and Observatoire Moana to obtain a more precise estimate of the orbital period. We derived the orbital and physical parameters through a joint analysis of these data. Results. We report the discovery and characterization of TIC65910228 b, a transiting warm Jupiter with a mass of 4.52 ± 0.26 M J and a radius of 1.070 ± 0.049 R J , orbiting an evolved F-type star every 180.5241 ± 0.0009 days in an eccentric orbit ( e = 0.26 ± 0.04). Conclusions. This planet joins a currently underexplored population of long-period ( P > 100 days), massive ( M p > 4 M J ), transiting giant planets, figuring as one of the few exhibiting a mild eccentricity. This target is a fine example of the potential of single-transit events to populate this region of the parameter space.