0 Assigned ID: 4956 ----- Attempting Submission 1 (Tue Feb 06 20:35:34 GMT 2024) ----- HST Phase I Proposal 4956 successfully submitted. Receipt: # 4956-1 ----- Attempting Submission 2 (Thu Feb 08 21:05:33 GMT 2024) ----- HST Phase I Proposal 4956 successfully submitted. Receipt: # 4956-2 0 ----- Attempting Submission 1 (Tue Feb 20 21:42:31 GMT 2024) ----- Late time UV spectroscopy of SN 2023ixf in M101: Unique constraints on the progenitor mass loss history We request 10 orbits of HST STIS UV spectroscopy to observe the nearby type IIP supernova 2023ixf in order to trace the late-time interaction between the ejecta and surrounding circumstellar material (CSM). Observations of nearby core collapse (CC) supernovae can teach us about the final years of massive stars in the run-up to their explosion, a portion of stellar evolution that is difficult to model. Some recent observations of type II supernovae have shown evidence for strong CSM interaction, implying that the red supergiant (RSG) progenitor star experienced 10^-3-10^-1 solar masses/year of mass loss in their final months, far higher than the 10^-6 solar masses/year seen in RSGs. To try to reconcile these measurements, observations in the nebular-phase are necessary (>=300 days) to probe material that was blown off the progenitor star decades before explosion. For this task, ultraviolet (UV) observations are more sensitive than the optical, where models predict strong Lyman alpha and MgII emission to trace CSM interaction strength. The recent discovery of SN2023ixf in M101 (~6.4 Mpc) gives us a unique chance to trace mass loss to late phases when the CSM interaction dominates in the ultraviolet. HST observations have shown that SN2023ixf, in the UV, experienced clear CSM interaction through 200 days after explosion. This non-disruptive ToO will observe SN2023ixf 300-400 days after explosion and complete our understanding of the mass loss and CSM interaction for a typical type IIP supernova. Given how close SN2023ixf is and the lifetime of HST, this is probably the finally opportunity to fill a crucial gap in our knowledge of the evolution of CC supernovae in the UV. This proposal will be triggered on SN 2023ixf a nearby SN discovered on 19 May 2023. We will observe the SN with STIS FUV-MAMA G140L observation with the 52x0.2" slit and STIS NUV-MAMA G230L observation with the 52x0.2" slit. The observations should be scheduled between March and April 2024 in the first window of observation to monitor the supernova at the appropriate phase and to ensure available guide stars for this field. Please execute all the visits as close as possible in time of so that we are able to combine this data for a time-varying object Ideally last visit should be within 3 weeks from first visit. visit 1 STIS FUV-MAMA G140L 2 orbits visit 2 STIS FUV-MAMA G140L 2 orbits visit 3 STIS FUV-MAMA G140L 2 orbits visit 4 STIS FUV-MAMA G230L 2 orbits visit 5 STIS FUV-MAMA G230L 2 orbits S. Valenti is the PI of this proposal. He has worked comprehensively on core collapse supernovae (CC SNe). K. A. Bostroem extensive experience with the STIS data reduction and the reduction and analysis of core collapse supernovae observations with Swift and Gemini. Her research focuses on understanding the progenitors of hydrogen-rich CC SNe. D. Sand is the co-PI of the DLT40 survey and an expert in the progenitors of Type Ia SNe and SN environments. He has extensive experience with Swift, and Gemini observations of SNe and their environments. J. Andrews is an active member of the DLT40 team, has expertise observing with HST/STIS, and is an assistent astronomer the Gemini Observatory. Her research focuses on characterizing the progenitors of core collapse (CC) SNe, specifically focusing on their mass-loss history via circumstellar interaction. M. Lundquist is an active member of the DLT40 team and specializes in the reduction and analysis of Gemini and TESS observations supplementary to this proposal. He is currently a staff astronomer at the W. M. Keck Observatory. Prior to joining the DLT40 team, he worked as a Gemini Science Fellow at the Gemini Observatories. G. Hosseinzadeh is an expert in early SN~Ia light curves and has experience analyzing early UV data. Y. Dong is an active member of the DLT40 team and has experience analyzing both CC~SNe and SN~I. Dr. A. P. Ravi is an active member of the DLT40 team and has experience analyzing CC~SNe. J. Pearson is an active member of the DLT40 team and has experience analyzing both CC~SNe and SN~I. Stellar Physics and Stellar Types 0 false SUPPORTED EXT-STAR SUPERNOVA TYPE II J2000 J2000 STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/NUV-MAMA Spectroscopic No No G230L 2376 Timing link suitability includes constraints ([02 After 01 by at most 14.0 days] [03 After 01 by at most 14.0 days]) The scheduling data was generated by CASM 32.0. CASM was run in Phase II mode. This is visit 1 of 5 that should be executed as close as possible in time to previous visit. 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