0 Assigned ID: 4429 ----- Attempting Submission 1 (Wed May 24 17:14:22 GMT 2023) ----- Submission 2 of phase II for HST GO-17415. Updating for new target and filters based on minor change request approved by Joel Green. 1851299474 ----- Attempting Submission 1 (Thu Sep 07 16:25:55 GMT 2023) ----- ----- Attempting Submission 2 (Wed Mar 13 21:59:40 GMT 2024) ----- There is now significant evidence that at least 10% of massive stars undergo substantial and impulsive mass loss within a few years of core-collapse. In particular, observations of interacting supernovae suggest that their progenitors undergo extreme episodes of mass-loss shortly before core collapse, creating a dense shell of circumstellar material (CSM). While most of our understanding of this link has come predominantly from hydrogen-rich supernovae, there is a growing population of SN initially classified as hydrogen free but with evidence of CSM interaction at later times. Here we propose to take advantage of HST sensitivity and angular resolution to observe the nearby (d=14.4 Mpc) Type Ib SN2019yvr and constrain the disappearance of its progenitor star and ongoing circumstellar interaction. SN2019yvr is only the second stripped envelope SN with a candidate progenitor detection in pre-explosion HST images, and 150 days post-explosion it began to shown signs of SN2014C-like interaction with a hydrogen-rich medium. We request new imaging in F438W and F555W to confirm the disappearance of its pre-explosion counterpart and determine whether it is interacting with CSM at large separations from the progenitor system, implying its progenitor system was losing mass thousands of years before core collapse. We propose to observe the site of the Type Ib supernova (SN Ib) 2019yvr with WFC3. This site was previously observed in 2017 with WFC3/UVIS F438W and F555W, which revealed the a point source consistent with being the supernova's counterpart. Our program will observe this same source more than 4 years after the explosion and determine whether it has faded or disappeared, consistent with predictions that it was the progenitor star of 2019yvr and exploded in 2019. To maximize time on-source within each orbit, we split our observations into two orbits of F438W and two of F555W, both using a 3-point line pattern to guarantee a high S/N detection of any potential counterpart as well as nearby sources that will aid in alignment and PSF reconstruction near the site of SN2019yvr. Combined with the requested FLASH in each exposure (FLASH=12 for F438W and no FLASH for F555W), this will also minimize the effects of CTE while maximizing the field observed around the host galaxy NGC4666. PI Kilpatrick, and Co-Is Auchettl, Drout, Tinyanont, and Villar are supernova experts. Kilpatrick has led several supernova-related HST programs. The PI and Co-Is together have published over 60 journal articles using HST data on either supernovae or other optical transients. Auchettl, Drout, and Kilpatrick are PhD astronomers and skilled supernova observers, while our team is using Pan-STARRS, ATLAS, Swope, Nickel, SOAR, Gemini, Keck, XMM-Newton, and VLA to observe the proposed target, other stripped-envelope supernovae, and supernovae with strong shock interactions. Stellar Physics and Stellar Types Stellar Populations and the Interstellar Medium 6 false false true false false false false false SUPPORTED STAR SUPERNOVA SUPERNOVA TYPE IB J2000 J2000 WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F555W POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false 1723751054074 The scheduling data was generated by CASM 32.1.3. 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