The Union3 Supernova Ia Compilation

High-redshift supernovae observed with the Hubble Space Telescope (HST) are crucial for constraining any time variation in dark energy. In a forthcoming paper (Rubin+, in prep), we will present a cosmological analysis incorporating existing supernovae with improved calibrations, and new HST-observed supernovae. We combine these data with most of the world's current literature data, and fit using SALT2-4 to create the Union3 Supernova compilation. We present a new analysis framework that allows non-linear light-curve width and color corrections, direct modeling of color dispersion, and a redshift-dependent host-mass correction.