Confirmation of the Low-eccentricity Warm Jupiter HD 278555 b with NEID

The study of warm Jupiters is crucial to understanding the processes that govern giant-planet formation and migration. These planets sit at the boundary between cold giant planets and hot Jupiters, and studying their orbital properties, including period, eccentricity, and spin–orbit alignment, can offer insights into their past evolution and migration histories. We report the discovery and confirmation of a transiting warm Jupiter, HD 278555 b, which was first detected as a single transit event in a light curve from the Transiting Exoplanet Survey Satellite (TESS). We confirm the planetary nature of the signal using additional TESS data and ground based radial velocity (RV) follow-up observations from the NEID spectrograph, and we characterize the planet via a joint fit to the transit and RV signals. HD 278555 b has a mass of 0.84^+0.10_−0.10 M_J and a radius of 0.980^+0.036_−0.035R_J, and orbits an F8-type star with a period of  28.84^+0.000045−0.000046 days and a very low eccentricity of  0.085^+0.047_−0.049. These orbital parameters suggest the planet had a quiescent formation history, and either formed in situ or formed beyond the ice line and underwent a smooth inward migration process such as disk-driven migration. This discovery adds to the growing population of well characterized warm Jupiters that will inform planet migration theory.