Quantifying the Transit Light Source Effect for AU Mic to Complement Hubble Transmission Spectroscopy of its Young Planet

AU Mic is a 30 Myr pre-main sequence M dwarf in the stellar neighborhood (d=9.7 pc) with two known warm Neptunes on 8.46 and 18.86-day periods, respectively. AU Mic is an active spotted star, and unocculted spots can introduce spurious transit depth variations seen in exoplanet transmission spectra, known as the Transit Light Source Effect. By studying ground-based photometry and stellar spectra out of transit, we independently constrain the spectral signatures of AU Mic’s starspots so we can correct their effect in the atmospheric observations of the planet. To model the combination of contemporaneous photometric and spectroscopic observations taken by different ground based observatories in the Las Cumbres Observatory network, we built a self-consistent statistical inference framework which jointly models multi-color photometric variability and normalized high-resolution NRES spectra parameterized by spot coverage fraction and temperature. Here we will present the results of this study which include robust constraints on spot parameters and a discussion of how spot contamination will bias transmission observations of AU Mic b.