0 Assigned ID: 7055 ----- Attempting Submission 1 (Tue Apr 14 08:17:25 GMT 2026) ----- HST Phase I Proposal 7055 successfully submitted. Receipt: # 7055-1 ----- Attempting Submission 2 (Wed Apr 15 12:35:55 GMT 2026) ----- HST Phase I Proposal 7055 successfully submitted. Receipt: # 7055-2 ----- Attempting Submission 3 (Thu Apr 16 12:32:17 GMT 2026) ----- HST Phase I Proposal 7055 successfully submitted. Receipt: # 7055-3 ----- Attempting Submission 4 (Thu Apr 16 16:20:27 GMT 2026) ----- 0 ----- Attempting Submission 1 (Sun Aug 09 08:40:01 GMT 2026) ----- It keeps getting better: Supernova 1987A entering its fourth decade SN 1987A, the brightest supernova (SN) since 1604, is the great supernova (SN) of the HST era. HST has monitored the evolution from the very beginning, providing astronomers with a unique observational record of a SN evolving into a remnant. The most recent observations show major changes in the interaction with the iconic triple-ring nebula of circumstellar material on a time scale of one year. A strong increase of flux has been observed as the dense, inner ejecta of processed material have started to crash into the equatorial ring, while the shocks further out in the system are gradually revealing the mass-loss history of the progenitor star. Furthermore, JWST has recently detected the first clear electromagnetic signal from the compact object created in the explosion, though its properties are yet to be determined. We request imaging in narrow and broad filters over the next three cycles to study the evolution of the shock interaction and compact object. The observations will be used to measure the density profile of the inner ejecta, determine the mass-loss history of the progenitor, and constrain the main competing scenarios for the compact object (thermally emitting neutron star or pulsar-wind nebula). These investigations offer a unique avenue for connecting late stellar evolution, SN physics and compact objects. The HST observations are also indispensable for interpreting other multiwavelength observations of SN 1987A. These observations are a part of a 3-year mointioring program of SN 1987A (cycles 34, 35 and 36) using WFC3/UVIS. We will use the narrow filters F502N and F657N in all three cycles, where F502N will primarily be used to monitor the new interaction region in [O III] and F657N to track the expansion of the reverse shock. We will also use F625W in all three cycles, which probes the overall evolution of the structure of the remnant and connects to the previous long-term monitoring. The F438W filter will be used every 2nd year (Cycles 34 and 36) to monitor the color evolution. We will use the F763M filter in Cycle 35 to search for emerging emission from the compact object. To obtain a similar or better S/N as the previous observations, considering the fading of most regions of the remnant, we require two orbits each for F438W, F625W, F657N, and F763M, and four orbits for F502N. This amounts to 10 orbits per cycle with the cadences described above. Since 2003, all HST imaging have used a fixed dither strategy to improve spatial resolution, which will be repeated for consistency. We have placed an ORIENT constraint on the WFC3 imaging to make sure that the diffraction spikes from Stars 2 and 3 (Fig 1) do not overlap with the emission from the SN. The spikes are brightest in F438W, F502N, and F625W, but having the same orientation in all imaging observations will reduce systematic effects in the comparison between filters and epochs. Our team has extensive experience in HST observations of SN 1987A, with many of the team members having been involved since the launch of HST. Co-PIs J. Larsson and C. Fransson have been leading these efforts in recent years. The expertise within the team covers everything from HST data reduction and analysis to theoretical modeling. Many of the team members are also involved in other multiwavelength observations of SN 1987A, including JWST, VLT and ALMA. J. Larsson will lead the data analysis of the proposed observations, while C. Fransson will lead the theoretical modeling. Stellar Physics and Stellar Types 6 false false false false false false false SUPPORTED EXT-MEDIUM SNR This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 The scheduling data was generated by CASM 34.0. CASM was run in Phase I mode. WFC3/UVIS Imaging No No F625W WFC3/UVIS Imaging No No F657N WFC3/UVIS Imaging No No F502N WFC3/UVIS Imaging No No F438W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false /Users/jlarsson/astro/proposals/hst/87a_2026/phase2_cycle34/OP-cache/phase2_87a_cycle34-v01.xml Timing link suitability includes constraints ([Sequence (01 02 03) within 30.0 days]) The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. The orienation constraints are set to make sure that the diffraction spikes from the bright nearby stars do not overlap with the emission from the SN. The timing requirement is to keep the appximate one year cadence of the monitoring. 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