0 Assigned ID: 6330 ----- Attempting Submission 1 (Thu Apr 10 00:36:54 GMT 2025) ----- HST Phase I Proposal 6330 successfully submitted. Receipt: # 6330-1 ----- Attempting Submission 2 (Thu Apr 10 09:15:57 GMT 2025) ----- HST Phase I Proposal 6330 successfully submitted. Receipt: # 6330-2 ----- Attempting Submission 3 (Thu Apr 10 09:46:38 GMT 2025) ----- updated coordinates 1580500502 ----- Attempting Submission 1 (Wed Aug 06 09:24:48 GMT 2025) ----- ----- Attempting Submission 2 (Thu Mar 12 10:04:35 GMT 2026) ----- FUV imaging of massive Magellanic Clouds clusters Stripped stars are one of the most exciting types of massive binary interaction products. They are the hot, helium-rich cores of intermediate and high-mass stars that have lost their envelope through mass transfer or common-envelope evolution. Stripped stars dramatically enhance the ionization radiation budget of massive stars and are excellent candidate progenitors of hydrogen-poor core-collapse supernovae. Given their temperature and small sizes, stripped stars are hard to detect in the optical. Using NUV SWIFT photometry, a newly proposed method, based on NUV-optical color-indexes, has recently been successful in identifying a dozen such stripped stars in the Magellanic Clouds (MCs). However, the quality of the PSF and its photometric precision have limited these studies to low-density field regions, and to more massive stripped stars with no or optically-faint companions. Here we propose to take the detection of stripped stars to the next level, by testing and validating the use of HST FUV photometry in two 25-40 Myr massive MC clusters. As FUV photometry is challenging given Brightness Object Protection constraints, we used archival WFC3/F225W photometry and VLT/MUSE integral field spectroscopy to avoid problematic objects in the clusters targeted here. Characterizing the full stripped-star population is crucial to constrain binary evolution models and can only be achieved with FUV imaging. Our pilot project will open the possibility to detect stripped stars in their native clusters (hence assign them an age!), particularly stripped stars with optically bright companions (unidentifiable in the NUV or optical) and lower-mass stripped stars than possible so far. We aim to obtain deep STIS.MAMA FUV F25QTZ imaging at 4 positions in 2 different clusters in the magellanic clouds to: - identified stripped stars in dense environments - characterise the FUV crowding of sources in the MCs to prepare the upcoming UVEX mission Using archival mF225W data (published in Milone+2018,2023), we identified these positions so that no stars is brighter than mF225w=13.5 Using ground-based integra-field spectroscopy (Bodensteiner+2022 for NGC330; unpublished for NGC1818), we check that there are no O-type stars in the field of view. The combination of these two requirements (Teff<30kK and mF225w) allow us to guarantee to safety of the instrument. We also check the total count rate by integrating the source fluxes over the FOV and found out that the global count rate of the detector stays <10 000 cnt/s We plan 1 orbit per position. Given we don't need particular acquisition, we have a ~2400sec integration duration that we split into 2 sub-exposure dither by 2arcsec to correct for cosmic and detector defects. We aim to reach sources with (Vega)MagFUV = 23 (ABmag~24.5) at 5sigma. The team has expertise in all aspects needed for the present projects, including past experience with HST/WFC3, crowded-field photometry, stellar evolution, and dust extinction. Sana and Bodensteiner are experts in observing massive stars with various ground and space instruments. Bodensteiner is the PI of the MUSE observations to reject O type stars Ludwig is experienced in SWIFT UV photometry in the Magellanic Clouds, including PSF fitting in dense fields, and has been driven the search for stripped stars in the Magellanic Clouds Willcox is expert in rapid binary population synthesis (e.g. COMPASS) whil Marchant is an expert in details code (eg MESA). Together, they will create dedicated simulations to compare the results of this campaign. Stellar Physics and Stellar Types 6 false false false false false false false SUPPORTED STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 mF225>13.5 VEGAMAG STELLAR CLUSTER OPEN CLUSTER J2000 J2000 mF225>13.5 VEGAMAG STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 mF225>13.5 VEGAMAG STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 mF225>13.5 VEGAMAG STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 mF225>13.5 VEGAMAG STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 mF225>13.5 VEGAMAG STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 mF225>13.5 VEGAMAG STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 mF225>13.5 VEGAMAG STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25QTZ STIS/FUV-MAMA Imaging No No F25QTZ /private/var/folders/6c/hg_c918n3njgc61v2nlkh2v4dpknxl/T/OPVisit12915322007364942284.xml The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 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