Spectroscopic Starspot Filling Factor Measurements with APOGEE

We present a large sample (~135,000) of two-temperature star spot filling factor measurements for the intersection of APOGEE DR17 and Gaia DR3 on the lower main sequence. These infrared spectroscopic starspot detections are tied to the intrinsic activity of the star and its dynamo. We show the existence of a Rossby scaling comparable to that for other activity diagnostics, and that large star spot filling factors are the norm and not the exception for active stars. We demonstrate that including star spots at the level seen in the data leads to more accurate stellar parameters in the era of precision stellar astrophysics, with strong shifts in derived effective temperature, radius, and age. This work has broad applications as it makes starspot measurements accessible for a large fraction of the sky, with immediate applications in stellar parameter estimation and exoplanet characterization/habitability.