0 Assigned ID: 2247 ----- Attempting Submission 1 (Fri Apr 09 21:07:30 GMT 2021) ----- 0 ----- Attempting Submission 1 (Fri Jul 23 16:16:52 GMT 2021) ----- Unveiling the nature of interacting supernovae or supernova impostors Some apparent supernovae (SNe) with strong circumstellar interaction are likely the explosion of very massive stars. Surprisingly, a significant fraction of these explosions is preceded by outbursts from weeks to years before. When and why outbursts herald terminal SN explosions is still unknown. Moreover, in some cases, it is not even clear whether the star has undergone a terminal SN explosion or has rather experienced an extreme, but non-terminal, eruption as a "supernova impostor''. To answer these questions, we must first obtain clear evidence that these stars have indeed undergone a core-collapse supernova explosion. We propose to use HST+WFC3 to visit the field of four of these transients after they have faded to obtain a deep, high-resolution image. This will allow us to search for (or place limits on) any surviving stellar progenitor and hence test whether these are terminal explosions or not. Our HST observations will focus on sampling the entire spectral energy distribution of four nearby (<30 Mpc) supernova (SN) impostors with deep imaging of their sites in the most similar filters to those used at the pre-discovery observations. We are looking to compare magnitude changes without an additional source of error from large color terms and set a robust limit on the bolometric luminosity of any source at the transient. (1) We will observe the SN 2015bh site using WFC3/UVIS with F438W, F606W and F814W and a pattern of 3 dither positions to achieve a 5sigma detection at > 26 mag. Similarly, we estimate we can reach a 4.5sigma limiting magnitude at H ~25 using WFC3/IR with F160W. Allowing 6.5 min for target acquisition and ~13 min per intermittent overheads and pointing maneuvers, we calculate ~53 min for 2 exposures per each UVIS filter, which is within the visibility for an orbit. Similarly, we estimate the reminding WFC3/UVIS observations and F160W, accounting for readout, guide-star, (re)-acquisition and switching between UVIS and IR channels, will take approximately 53 minutes, again within a single orbit. (2) We request F350LP, F555W and F814W images of the AT 2016jbu's site using WFC3/UVIS, reaching between 5 and 10sigma at > 26 mag. Additionally, we will obtain images in the IR using WFPC3/IR in the F160W filter. Considering target acquisition, overheads and pointing maneuvers, we need 2 orbits again. (3) We will observe SN 2013gc in F438W, F606W and F814W, with the addition of F160W. We estimate observations in these four filters while aiming to achieve a 5sigma limiting magnitude at ~25 mag, accounting for readout, guide-star, (re)-acquisition and switching between UVIS and IR channels, will be obtainable within 2 orbits. (4) SN 2009ip will also be observed with F438W, F606W, F814W using WFC3/UVIS, and F160W using WFC3/IR. Allowing for the necessary overheads, this is achievable within 2 orbits. We, therefore, use 8 orbits to obtain observations of our SN 2009ip-like transient sample. We use point dithering to correct for cosmic rays and hot pixels and to improve the sampling of the point spread function. We exploit the entire detector in each case, placing our targets in the optimal position on the chips according to their location in the host galaxy. For each case, we have sought a compromise between having the highest number of reference stars with a high enough S/N for accurate astrometric registration. Our team combines expertise in the observation and study of core-collapse SNe and SN impostors. We also have a large experience in the research on SN progenitors and the use of HST images. We will use using standard imaging techniques on HST data. Stellar Physics and Stellar Types 6 false false false false false false false false SUPPORTED STAR LUMINOUS BLUE VARIABLE SUPERNOVA This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR LUMINOUS BLUE VARIABLE SUPERNOVA This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR LUMINOUS BLUE VARIABLE SUPERNOVA This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR LUMINOUS BLUE VARIABLE SUPERNOVA This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F555W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 3 false POS-TARG DITHER 0.605 LINE false false 3 41.788 WFC3-IR-DITHER-LINE-3PT 4 false /Users/ner/ownCloud/work/ToDo/HST_phase2/OP-cache/phase2_v5-v01.xml The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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