2025ApJ...993..138D

Extreme ultraviolet (EUV; 100-912 Å) photons influence the formation and evolution of planets by ionizing hydrogen and other species, but the EUV radiation of most exoplanet host stars is poorly constrained. This work applies the differential emission measure (DEM) technique to infer the EUV spectra of eight stars previously observed with high signal-to-noise ratios by the Extreme Ultraviolet Explorer (EUVE; 1992-2002) spanning spectral types from M to F: AD Leo (MV), ${ \mathcal E }$ Eri (KV), κ¹ Ceti (GV), Procyon (FIV-V), α Cen A + B (GV + KV), and ξ Boo A + B (GV + KV). The model spectra are accurate to within a factor of 3 for the majority of individual EUVE flux density data points and accurate to within 30% of the integrated 100-300 Å fluxes. We provide the atomic data used for each star's calculations, X-ray/EUV/far-ultraviolet (noncontemporaneous) observational inputs, the DEM models, and the model-predicted EUV spectra (extending beyond the 90-510 Å range of the EUVE spectra) and compare the results to archival EUVE data. We also find that the relative contributions of the transition region and corona to a star's EUV emission vary significantly among the few stars analyzed here. The flare-driven variability of the corona is greater than the transition region, so the EUV spectrum of each star will have stochastic flare excess contributions at different wavelengths depending on the star's temperature structure, flare behavior, and activity cycle. We conclude with a discussion of the implications of this variability for analyses that use EUV estimates to study planetary atmospheric evolution.