typo correction 168981946 Your proposal could not be saved. Submission aborted. Assigned ID: 6162 ----- Attempting Submission 1 (Tue Apr 08 16:06:29 GMT 2025) ----- HST Phase I Proposal 6162 successfully submitted. Receipt: # 6162-1 ----- Attempting Submission 2 (Wed Apr 09 14:54:21 GMT 2025) ----- HST Phase I Proposal 6162 successfully submitted. Receipt: # 6162-2 ----- Attempting Submission 3 (Wed Apr 09 15:04:10 GMT 2025) ----- HST Phase I Proposal 6162 successfully submitted. Receipt: # 6162-3 Have removed the noninteruptabel sequence 1902822422 ----- Attempting Submission 1 (Thu Aug 14 09:28:22 GMT 2025) ----- HST Phase II Proposal 18024 successfully submitted. Receipt: # 18024-1 ----- Attempting Submission 2 (Thu Aug 14 10:08:28 GMT 2025) ----- HST Phase II Proposal 18024 successfully submitted. Receipt: # 18024-2 ----- Attempting Submission 3 (Thu Aug 14 10:12:09 GMT 2025) ----- HST Phase II Proposal 18024 successfully submitted. Receipt: # 18024-3 ----- Attempting Submission 4 (Thu Dec 04 09:10:43 GMT 2025) ----- Untangling the stellar content of the NGC 6822 Hubble regions with the unique WFC3/IR filters With the unique WFC3/IR medium band filters we will image massive star-formation regions (Hubble I/III, IV, V, X) in the low-metallicity dwarf galaxy NGC 6822. These regions, spanning various evolutionary stages, provide a temporal sequence of star formation under conditions analogous to the early Universe. This high-resolution HST data will be combined with existing JWST and ALMA observations to study star formation, stellar feedback, and dust evolution in this system. A central challenge is distinguishing young stellar objects in the Hubble regions from the significant population of evolved stars in the NGC 6822 field, which overlap in colour space. The unique WFC3/IR filters, sensitive to H2O absorption in M-type AGB stars and the CN+C2 features in Carbon stars, break this degeneracy. It will even determine AGB star chemistries from which we can quantify their dust production. Given the significant roles of evolved stars in the chemical enrichment of the interstellar medium (ISM) and young massive stars in shaping their environments through intense radiative feedback, jets and winds, detailed observations of the interplay of these populations in nearby systems where CO cores and atomic gas have also been resolved on 1--3 pc scales is essential. By characterizing the stars physical properties via SED modeling and their effects on the HII regions in NGC 6822, we can refine our understanding of massive star formation and the dust lifecycle in chemically unenriched environments. We are imaging four metal-poor star-forming (SF) regions (Hubble I/III, Hubble IV, Hubble V, and Hubble X) with WFC3/IR medium band filters . Our observations aim to conduct a census of massive young stellar objects (YSOs) and asymptotic giant branch (AGB) stars, and characterize their properties with spectral energy distribution (SED) model fitting in effort to better understand star formation and dust production mechanics, as well as massive star cluster evolution, in an extragalactic system which mimics the metal-poor nature of early-universe SF galaxies. Filters: To take full advantage of the CN+C2 and water features near 1.4 microns, we require observations with F127M, F139M, and F153M. All three filters are necessary, since combinations with the broad-band optical, near-IR, and IR filters do not successfully isolate the carbon stars. Required exposure times and photometric depth: To detect all AGB stars, we must achieve full photometric completeness at the tip of the red giant branch (TRGB). The orbit time for our target is 52 min, so we can achieve the necessary photometric depth within a single orbit (as demonstrated by Boyer et al. 2013). This allows for total exposure times of 700-800s in each filter, resulting in S/N > 10 in F127M for Ko=17.5mag, using a Bruzual template for an M6III star, simulating a TRGB star in the galaxy. Dithering Strategy: Dithering diminishes errors associated with where a source is placed on a pixel, undersampling of the WFC3/IR channel, and image artifacts such as cosmic rays. We choose a 4-point dithering strategy to acheive Nyquist sampling of the PSF & to simultaneously allow us to fit the three selected filters into a single orbit. We have entered the dither offsets manually into the target offset entries following the WFC3 handbook WFC3-IR-DITHER-BOX-MIN values from table C.3 Parallels: There are no parallel observations for this program. Scheduling Constraints: There are no scheduling constrains for this program. Our team has experience in IR imaging of resolved stellar populations and associated data analysis methods, attained from HST, Spitzer, JWST and Herschel. All necessary software, analysis, and data dissemination tools are in place and tested, maximizing the efficiency of our scientific program. PI Dr. Olivia Jones is a Webb fellow who is an expert on infrared imaging and spectroscopy of stars in the Local Volume. She is has uses these WFC3/IR medium band filters to search for carbon stars in the compact galalxy M32 and has extensivly studied the youn and old population of MGC 6822 with JWST and Spitzer. PI Conor Nally is an expert on photometric data processing of resolved stellar photometry of crowded stellar fields having worked on large data sets of this and similar targets and will coordinate the science effort. CoI Dr. Martha Boyer has extensive experience with optical/IR observations of Local Group galaxies with HST, Spitzer, and JWST. She is an expert in IR stellar populations and AGB stars and established and widely executed the technique outlined in the proposal. CoI Prof. Annette Ferguson is an expert in local group galaxies and resolved stellar populations. She has extensive experience observing, reducing and analysing HST data. CoI Dr. Margaret Meixner is an expert in the analysis and interpretation of infrared (IR) photometry of dusty and evolved stars in nearby dwarf galaxies and has published extensively on the physics and chemistry of interstellar dust and gas. CoIs Dr. Isha Nayak, Dr. Nolan Habel, Dr. Alec Hirschauer, Jess Howell, Dr. Patrick Kavanagh, Dr. Laura Lenkic are experts in optical and IR imaging of stellar populations in dusty environments with extensive experience with image processing, photometric reduction and analysis techniques. 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NSAMP = 8 -Using a 4pt dither for F127M, F139M and F153M. -Exposures arranged to avoid latency due to buffer dump. -Total of one orbit (Tic-Visit :proposal-id 18024 :visit-id "03" :proposal-version -1 :trans-version "20250624" :date "04-Dec-2025 09:57:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1827984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18024 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18024 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2532 :al-overhead-at-end 0 :internal-dur-at-end 709 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2974 :pcs-gap 0 ) true 1 0 /private/var/folders/jy/1lj471j963jfs8t0q2lssy980000gq/T/OPVisit17151534026993579121.xml The scheduling data was generated by CASM 33.1. 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