0 Assigned ID: 4769 ----- Attempting Submission 1 (Wed May 24 22:49:33 GMT 2023) ----- HST Phase I Proposal 4769 successfully submitted. Receipt: # 4769-1 ----- Attempting Submission 2 (Wed May 24 23:26:23 GMT 2023) ----- HST Phase I Proposal 4769 successfully submitted. Receipt: # 4769-2 ----- Attempting Submission 3 (Wed May 24 23:32:52 GMT 2023) ----- HST Phase I Proposal 4769 successfully submitted. Receipt: # 4769-3 ----- Attempting Submission 4 (Wed May 24 23:49:26 GMT 2023) ----- HST Phase I Proposal 4769 successfully submitted. Receipt: # 4769-4 ----- Attempting Submission 5 (Wed May 24 23:55:18 GMT 2023) ----- The IMF is foundational to large swaths of astrophysics and offers a fundamental test of star formation models. There are strong theoretical arguments, and a growing number of observational clues, that the IMF should vary as a function of environment. These variations should be strongest at the high-mass and low-mass extremes, including the production of planetary-mass brown dwarfs (<15 MJup), but this remains untested since only modest numbers of planetary-mass BDs have been found, mostly in sparse nearby populations. HST has taken wide-field mosaics in five much denser and more massive clusters using WFC3-IR in Drift-and-SHift ("DASH") mode to completely encompass their entire spatial extent, and using multicolor imaging (F110W, F160W, and F139M) to distinguish young brown dwarfs from reddened field interlopers via water absorption in F139M. However, detection limits in these mosaics are currently >20 MJup due to a severe readnoise penalty inherent to the standard DASH analysis method. We propose to develop and publicly release a new method of analyzing WFC3-IR DASH images: PSF-DASH, which forward-models directly into drifting datacubes in order to optimally mitigate readnoise. This method will extend DASH surveys up to 1.5 magnitudes deeper, achieving a sensitivity boost that would be observationally prohibitive. We will then apply PSF-DASH to archival observations of these 5 clusters, identifying cluster members well into the planetary-mass regime (5-8 MJup), quantifying the slope/normalization/cutoff of the low extreme of the IMF, identifying IMF variations in comparison to local sparse associations, and selecting robust samples for JWST spectroscopic followup. Dr. Adam Kraus is an expert in star and planet formation and in the demographics of young stars. He was the PI of program HST-GO-15238, which executed the observations that will be analyzed, and he has coordinated the analysis and interpretation of all observations using classic DASH-mode data analysis. After finding that the IMFs did not reach the depth needed to achieve many of the science goals, he developed much of the framework behind PSF-DASH and wrote the alpha software. However, this effort was not scoped into HST-GO-15238. Dr. Will Best is an expert on the demographics of brown dwarfs and the low-mass end of the IMF. He has been a key member of the analysis team for HST-GO-15238, leading the analysis and interpretation of the classic DASH-mode data analysis. He is lead author of the catalog paper reporting the source lists of those observations and the paper that interprets the IMF and spatial distributions of these regions in the M dwarf and high-mass brown dwarf regime. Stellar Physics and Stellar Types Stellar Populations and the Interstellar Medium 0 Regular false false false false false false SUPPORTED