0 Assigned ID: 6536 ----- Attempting Submission 1 (Thu Apr 10 17:10:35 GMT 2025) ----- HST Phase I Proposal 6536 successfully submitted. Receipt: # 6536-1 ----- Attempting Submission 2 (Thu Apr 10 17:18:08 GMT 2025) ----- HST Phase I Proposal 6536 successfully submitted. Receipt: # 6536-2 ----- Attempting Submission 3 (Thu Apr 10 21:52:56 GMT 2025) ----- HST Phase I Proposal 6536 successfully submitted. Receipt: # 6536-3 ----- Attempting Submission 4 (Thu Apr 10 21:55:17 GMT 2025) ----- ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN Initial draft plan for our program for review by Alison Vick. Small deviations from our initial Phase 1 plan to minimize orbital visibility overrun that was present in new APT version. This includes: * shortening short exposures from 45s/60s to 35s in all cases. These exposures are to enable measurements of saturated stars. * eliminating one F467M exposure from the second orbit of HVS7 observations Resubmission Aug 16 2025 to fix problem with switching specified aperture to UVIS for all NGC1916 exposures. -153389714 ----- Attempting Submission 1 (Fri Aug 08 22:52:42 GMT 2025) ----- ----- Attempting Submission 2 (Sat Aug 16 23:07:29 GMT 2025) ----- All are small visibility overruns; all observations seem schedulable. Where is the central black hole in the LMC? The presence of massive black holes remains poorly constrained in dwarf galaxies, especially in the late-type dwarfs that dominate the population. The nearest late-type dwarf galaxy, the Large Magellanic Cloud (LMC), is an important case in point. Despite its proximity, the presence of a massive black hole in the LMC remains unsettled, largely because of the uncertainty in the location of the center of this tidally disturbed galaxy. The recent discovery of a population of hypervelocity stars emanating from the central regions of the LMC strongly suggest that a massive black hole is present, but its location is poorly constrained. We will address this in two ways: first, we will obtain new HST imaging for two LMC hypervelocity stars, combining these data with Gaia to measure ultra-precise proper motions and localize their origin near the LMC's center a factor of 9 better than existing constraints. Second, we will obtain new imaging of NGC1916, the most likely nuclear star cluster of the LMC. When combined with archival HST data, this will allow us to measure high-precision proper motions (~3 km/s), enabling clean identification of cluster members. With this data we will weigh any black hole in this cluster through both dynamical modeling and the possible identification of any fast stars near the black hole. If a massive black hole is present in the LMC, these proposed observations offer the best chance to both reveal it and constrain its mass. Exposure time strategies: NGC1916 -- matching previous observations in F555W and F814W with 10x exposure time differences for optimal proper motion determination. Getting F438W observations for stellar populations distinctions. F814W: 3x35s + 4x350s F555W: 3x35s + 5x350s F438W: 3x35s + 3x670s HVS3 --Match previous observation filter to obtain 10x350s exposures in F850LP (30% saturation); we will also take 3x45s in F814W (15% saturation); these can mitigate potential issues with the distortion solution in F850LP. HVS 7 -- For filter consistency, we will obtain 4x35s and 5x350s (9%/90% saturation) in F606W, and 4x440s in F467M (30% saturation), which has an accurate distortion solution & PSF. Dither pattern are used with POS TARGS; for targets with 3/4/5 exposures per filter we use a dither sequence that gets 0.5 pixel dithers in x/y/x&y along with integer pixel dithers to make sure hot pixels don't impact more than a single exposure. For HVS3, the 10 exposures use a 1/3rd pixel offset grid for the first 9 exposures and then use 1/2 pixel offset. These are added to integer pixel offsets. Flash set to near the minimum values to reduce CTE issues for all exposures. We have assembled a team with a wide range of expertise as part of this proposal. The core measurements in this proposal are proper motions, and we have several experts on our team. This includes Maximilian Haeberle, Florian Niederhofer, and Kevin McKinnon. Max and Florian have deep experience in deriving HST proper motions in star clusters including those in the LMC (Niederhofer et al. 2024) and the discovery of massive black holes with proper motion data (Haeberle et al. 2024). Kevin McKinnon has written the BP3M code (McKinnon et al. 2024) that enables optimal combination of Gaia and HST astrometry. It is provides robust absolute proper motions and error bars in precisely the situations exhibited with the HVSs in this proposal; using a handful of Gaia stars combined with HST data. Jesse Han did the HVS orbital modeling presented in the proposal and discovered the population of HVSs with an LMC origin in Han et al. 2025. He will translate proper motion measurements into the constraints on the localization of the black hole in the LMC. Scott Luchinni has done LMC orbital simulations that have gone into this work. Sebastian Kamann is PI of the MUSE data for NGC1916 and graduate student Elena Balakina is undertaking ongoing analysis of this data. Cliff Johnson, and Nate Bastian are also experts on star cluster stellar populations. Arash Bahramian Jay Strader, and Eric Koch are conducting multi-wavelength follow up of potential black holes in the LMC including the X-ray and (not discussed in the proposal due to space limitations) radio detection of NGC1916. Anil Seth and Nadine Neumayer are experts dynamical measurements of black holes in dwarf galaxies and PIs of the oMEGACat project which includes extensive analysis of MUSE+HST datasets on our nearest nuclear star cluster (7 papers over the past 2 years). Stellar Populations and the Interstellar Medium Supermassive Black Holes and Active Galaxies 6 false false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 EXT-STAR B0-B2 III-I J2000 J2000 aka HE 0437-5439 EXT-STAR B3-B5 III-I J2000 J2000 G=17.934, BP-RP=-0.105 WFC3/UVIS Imaging No No F850LP WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F467M WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F438W /private/var/folders/_m/t72qk349343b2hlsz5bs5x4r0000gp/T/OPVisit1420206952571370681.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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