Validation of HD 183579b Using Archival Radial Velocities: A Warm Neptune Orbiting a Bright Solar Analog

As exoplanetary science matures into its third decade, we are increasingly offered the possibility of pre-existing, archival observations for newly detected candidates. This is particularly poignant for the TESS mission, whose survey spans bright, nearby dwarf stars in both hemispheres—precisely the types of sources targeted by previous radial velocity (RV) surveys. On this basis, we investigated whether any of the TESS Objects of Interest (TOIs) coincided with such observations, from which we find 18 single-planet candidate systems. Of these, one exhibits an RV signature that has the correct period and phase matching the transiting planetary candidates with a false-alarm probability of less than 1%. After further checks, we exploit this fact to validate HD 183579b (TOI-1055b). This planet is <4 R⊕ and has better than 33% planetary mass measurements, thus advancing TESS' primary objective of finding 50 such worlds. We find that this planet is among the most accessible small transiting planets for atmospheric characterization. Our work highlights that the efforts to confirm and even precisely measure the masses of new transiting planet candidates need not always depend on acquiring new observations—in some instances, these tasks can be completed with existing data.