0 Assigned ID: 2196 ----- Attempting Submission 1 (Fri Apr 09 20:16:23 GMT 2021) ----- Type Ia supernovae (SN Ia) are explosions of white dwarfs, critical to measuring cosmological distances. Despite their importance, the precise progenitor type, specifically their pre-explosion mass, remains unknown. Early supernova light curves are powered by the 56Ni decay chain and do not disagree with progenitor models. However, at very late times (>1000 days) the supernova is mainly powered by the neutron-rich isotopes 57Ni and 55Co. The abundances of 57Ni and 55Co are strongly correlated with the central density and thus mass of the exploding white dwarf. Ergo late time observations of SNe Ia (>1000 days) have the power to discriminate between progenitor scenarios. We propose to answer the progenitor question by enhancing the open-source TARDIS radiative transfer code with the necessary physics, and a subsequent Bayesian parameter inference of the 57Ni/55Co abundance, using the Hubble Space Telescope photometric observations of the only five SNe Ia that have been observed that late. Specifically, we will modify TARDIS to add nuclear decay as the energy deposition source. We will extend the ionization and excitation treatment of TARDIS with additional effects. A time-dependent extension is required for the delayed energy deposition. For the 57Ni/55Co abundance inference from the photometric observations we will use machine learning-based emulators and Bayesian statistics. Our proposal will, for the first time, combine all known important effects for modeling the late phase into one simulation, and will also use rigorous statistical parameter inference to produce firm conclusions on the decades-long outstanding progenitor problem of SNe Ia. Drs. Fullard, Kerzendorf, Floers and Vogl, and Mr. Williamson, are experienced astronomical software developers with extensive knowledge of radiative transfer. Kerzendorf, Pakmor, and Floers are experienced in Type Ia supernova theory and models. Graur and Kerzendorf are experts on SNe Ia observations specifically using Hubble (led several observing campaigns). Kerzendorf, Williamson, and Vogl are experts on Bayesian inference using high fidelity codes. Dr. Andrew Fullard will serve as the science PI of this program and Dr. Wolfgang Kerzendorf will serve as the administrative PI. Stellar Physics and Stellar Types 0 Regular false false false true false SUPPORTED