Measuring the Effect of Progenitor Metallicity on Type Ia Supernova Distance Estimates

Typo fixes and minor edits 445694044 Assigned ID: 3506 ----- Attempting Submission 1 (Fri Mar 25 20:25:35 GMT 2022) ----- HST Phase I Proposal 3506 successfully submitted. Receipt: # 3506-1 ----- Attempting Submission 2 (Fri Mar 25 21:15:46 GMT 2022) ----- HST Phase I Proposal 3506 successfully submitted. Receipt: # 3506-2 ----- Attempting Submission 3 (Fri Mar 25 22:05:35 GMT 2022) ----- This target is not used in this proposal. This target is not used in this proposal. This target is not used in this proposal. Prepared visit 3 with observation of SN 2023lnh 836474370 ----- Attempting Submission 1 (Tue Jun 28 22:47:00 GMT 2022) ----- HST Phase II Proposal 17170 successfully submitted. Receipt: # 17170-1 ----- Attempting Submission 2 (Wed Jun 29 18:20:33 GMT 2022) ----- ----- Attempting Submission 3 (Wed Feb 01 21:45:30 GMT 2023) ----- HST Phase II Proposal 17170 successfully submitted. Receipt: # 17170-3 ----- Attempting Submission 4 (Thu Feb 02 03:53:12 GMT 2023) ----- Your proposal could not be saved. Submission aborted. Your proposal could not be saved. Submission aborted. Your proposal could not be saved. Submission aborted. ----- Attempting Submission 5 (Fri Apr 21 15:38:36 GMT 2023) ----- ----- Attempting Submission 6 (Mon Jun 26 20:47:18 GMT 2023) ----- The orbit and visit planners have been run for the relevant visit for this ToO Measuring the Effect of Progenitor Metallicity on Type Ia Supernova Distance Estimates Despite using Type Ia supernovae (SN Ia) to precisely measure cosmological parameters, we do not know basic facts about the progenitor systems and explosions. Theory suggests that SN Ia progenitor metallicity is correlated with peak luminosity, but not how quickly it fades, which we use to calibrate the luminosity and measure distances. This effect should lead to an increased Hubble scatter, reducing the precision with which we measure distances. If the mean progenitor metallicity changes with redshift or population, cosmological measurements such as the dark energy equation-of-state parameter and the Hubble constant could be biased. Models also indicate that changing progenitor metallicity will have little effect on the appearance of optical/NIR SN data, but significantly alter UV spectra. These data can only be obtained with HST. HST observations of 2 "twin" SN (having nearly identical optical spectra and light-curve shapes) with different UV spectra and peak optical luminosities indicate progenitor metallicity differences consistent with models. The current sample of SN Ia with near-peak spectra is siginificantly lacking in its representation of high-velocity (HV) SN Ia. To determine the overall impact of progenitor metallicity on cosmological measurements, we must increase this sample. The community now discovers ~20 SN Ia each year >2 weeks before peak. With the increased discovery rate of young SN, we can expect to observe 4 HV SN Ia in the UV in a single Cycle and constrain how velocity affects the diversity of SN Ia UV properties. This is our best opportunity to further our understanding of SN Ia while directly improving the utility of SN Ia for cosmology. There are 4 separate TOO targets, each will obtain a single spectrum. Each of these targets will require 2 orbits. Fast turn around is important, and we will work closely to speed this process up. Some tweaking to the visits will be required for each trigger. CoI Foley and his team have led several previous HST programs to obtain UV spectra of Type Ia supernovae. Foley has published 59 journal articles using HST data, including 10 on this topic. Foley, Brown, Dimitriadis, Filippenko, Fox, Jones, Kirshner, Pan, Rojas-Bravo, Siebert, Taubenberger, and Wheeler are all established supernova observers. They will contribute observational resources from several observatories to this study. Roepke, Sim, and Wheeler are accomplished supernova theorists who will produce models for this study. 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