Target SNII-1: There is no need or capability to test the scheduling of observations of generic targets in Phase I. This warning will go away the next time the proposal is loaded. Target SNII-2: There is no need or capability to test the scheduling of observations of generic targets in Phase I. This warning will go away the next time the proposal is loaded. 0 Assigned ID: 7376 ----- Attempting Submission 1 (Thu Apr 16 13:25:52 GMT 2026) ----- Visit planner warning for ToO targets. Phase 2 third submission. -1465875850 ----- Attempting Submission 1 (Tue Aug 18 15:09:40 GMT 2026) ----- HST Phase II Proposal 18418 successfully submitted. Receipt: # 18418-1 ----- Attempting Submission 2 (Wed Aug 19 13:56:13 GMT 2026) ----- HST Phase II Proposal 18418 successfully submitted. Receipt: # 18418-2 ----- Attempting Submission 3 (Wed Aug 19 14:29:26 GMT 2026) ----- A Far-UV Type II Supernova Treasury for the Upcoming UVEX Mission Ultraviolet (UV) spectroscopy of young type II supernovae (SNe II) in the first weeks post-explosion remains an almost completely unconstrained observational phase space. To date, only 2 published SNe II have been observed in far-UV (<1600 Angstroms) wavelengths in the first week post-explosion and no SN II with spectroscopic signatures of CSM-interaction at such wavelengths. In anticipation of the planned launch of the Ultraviolet Explorer (UVEX) NASA mission, we propose a disruptive ToO program to obtain FUV/NUV spectroscopy of 2 SNe II within their first 1-2 weeks post-explosion. This collection of STIS MAMAS (G140L and G230L gratings) observations will increase the number of young SNe II with FUV HST spectra by a factor of 2 and create a legacy UV dataset necessary for UVEX preparation. HST UV spectroscopy will enable robust constraints to be made on the chemical composition, density and extent of the progenitor star wind as well as the mechanisms for enhanced mass-loss in red supergiants during their final years. Furthermore, these observations will directly inform the creation of physically consistent non-LTE radiative transfer models of young SNe II that can be used to robustly interpret the large number of FUV SN II spectra expected from the UVEX mission. Far- and near-UV spectroscopy observations with STIS/MAMAS of two type II supernovae. Each target will need 3 epochs of observations (2 orbits per obs.). The first observation for each supernova should occur as soon after the ToO trigger as possible. The second and third epochs should occur ~2 days and ~4 days after the first epoch. Far and near-UV spectra observations per epoch need to be linked. Co-PI Wynn Jacobson-Galan has led a successful Flexible Thursday program during Cycles 31 and 32 and has extensive experience analyzing and reducing HST spectroscopic/photometric data. Dr. Jacobson-Galan is a NASA Hubble Fellow with significant expertise on the late-time light curves of supernovae observed with HST (2 published papers) and "flash spectroscopy" supernovae (5 published papers). Co-PI Dr. Luc Dessart is one of the world's leading experts on radiative transfer codes (CMFGEN) and hydrodynamics simulations (HERACLES). Both Co-PIs are members of the UVEX science team. Prof. Raffaella Margutti is a leading expert on x-ray and radio observations of interacting supernovae and is CCSN UVEX team lead. Profs. Mansi Kasliwal (UVEX GW team lead) and Ryan Chornock are experts in transient surveys and follow up of all types of explosive transients. Dr. Suvi Gezari is the Dynamic Universe Lead in the UVEX collaboration. Kaustav Das is a graduate student at Caltech supervised by professor M. Kasliwal (Co-PI of ZTF and lead of the ZTF EMGW group). His thesis focuses on the study of core collapse supernovae on the low mass end. Co-I Coughlin is an expert in optical survey filtering and telescope triggering. Dr. Aaron Tohuvavohu is an expert in UV telescope design. Our team has proprietary access to ZTF, a fast-cadence wide-area optical survey that is very well-suited to finding very young SNe. We have more than a decade of accumulated experience in identifying and following up very young SNe from both ground-based facilities and space-based ones (HST, Swift). We have access to a variety of robotic follow-up resources to help rapidly confirm the nature of any candidate transients, including the Palomar 60-inch telescope and the Liverpool Telescope; plus target-of-opportunity programs on classical facilities such as Palomar and Keck. Stellar Physics and Stellar Types 0 false true false false false false false SUPPORTED EXT-STAR SUPERNOVA TYPE II CSM interacting SN II EXT-STAR SUPERNOVA TYPE II CSM interacting SN II STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/FUV-MAMA Spectroscopic No No G140L 1425 STIS/NUV-MAMA Spectroscopic No No G230L 2376 /private/var/folders/7z/f0r022js1rb9rl1ldd_zhjww0000gn/T/OPVisit13324276587154940079.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. First epoch for target 1 -- needs to be observed as soon as possible after trigger (within the constraints of disruptive ToO policy). (Tic-Visit :proposal-id 18418 :visit-id "01" :proposal-version -1 :trans-version "20260618" :date "19-Aug-2026 10:18:03.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18418 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18418 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18418 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 ToO activation -- maximum response time is optimistic and can be iterated on. We hope for observations as soon as possible after trigger. /private/var/folders/7z/f0r022js1rb9rl1ldd_zhjww0000gn/T/OPVisit185978347118320000.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Second epoch for target 1 -- needs to be within 1-2 days of the first epoch. (Tic-Visit :proposal-id 18418 :visit-id "02" :proposal-version -1 :trans-version "20260618" :date "19-Aug-2026 10:29:14.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18418 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18418 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18418 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 ToO activation /private/var/folders/7z/f0r022js1rb9rl1ldd_zhjww0000gn/T/OPVisit10631760297287043891.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Third epoch for target 1 -- needs to be within 1-2 days of the second epoch. (Tic-Visit :proposal-id 18418 :visit-id "03" :proposal-version -1 :trans-version "20260618" :date "19-Aug-2026 10:21:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18418 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18418 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18418 :visit-id "03" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 ToO activation /private/var/folders/7z/f0r022js1rb9rl1ldd_zhjww0000gn/T/OPVisit8726073984619188035.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. First epoch for target 2 -- needs to be observed as soon as possible after trigger (within the constraints of disruptive ToO policy). (Tic-Visit :proposal-id 18418 :visit-id "04" :proposal-version -1 :trans-version "20260618" :date "19-Aug-2026 10:25:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18418 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18418 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18418 :visit-id "04" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 ToO Activation /private/var/folders/7z/f0r022js1rb9rl1ldd_zhjww0000gn/T/OPVisit1777453887267231115.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Second epoch for target 2 -- needs to be within 1-2 days of the first epoch. (Tic-Visit :proposal-id 18418 :visit-id "05" :proposal-version -1 :trans-version "20260618" :date "19-Aug-2026 10:24:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18418 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18418 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18418 :visit-id "05" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 ToO /private/var/folders/7z/f0r022js1rb9rl1ldd_zhjww0000gn/T/OPVisit12388127283982903600.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Third epoch for target 2 -- needs to be within 1-2 days of the second epoch. (Tic-Visit :proposal-id 18418 :visit-id "06" :proposal-version -1 :trans-version "20260618" :date "19-Aug-2026 10:29:14.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174832 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18418 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18418 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18418 :visit-id "06" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 ToO