The MUSCLES Extension for Atmospheric Transmission Spectroscopy

X-ray through infrared SEDs are essential for understanding a star's effect on exoplanet atmospheric composition and evolution. We present a catalog of panchromatic SEDs for 13 exoplanet hosting stars which have guaranteed JWST observation time as part of the ERS or GTO programs but have no previous UV characterization. The stars in this survey range from spectral type M-F (0.14-1.57M⊙) and ~4-132 days in rotation period (~0.5-11.4Gyr in age). The SEDs are composite spectra using data from the Chandra X-ray Observatory and XMM-Newton, the Hubble Space Telescope, BT-Settl stellar atmosphere models, and scaled spectra of proxy stars of similar stellar type and activity. From our observations, we have measured a set of UV and X-ray fluxes as indicators of stellar activity level. We compare the chromospheric and coronal activity indicators of our exoplanet-hosting stars to a broader population of field stars and find that a majority of our targets have lower activity levels than the average population of cool stars in the solar neighborhood. This suggests that using SEDs of known exoplanet host stars as proxies for the average population of stars in the solar neighborhood may underestimate the true high-energy flux environment by an order of magnitude or more. In this talk we present the data and methods used in the assembly of the composite panchromatic SEDs for the MUSCLES Extension targets.