0 Assigned ID: 5957 ----- Attempting Submission 1 (Tue Nov 05 16:54:02 GMT 2024) ----- HST Phase I Proposal 5957 successfully submitted. Receipt: # 5957-1 ----- Attempting Submission 2 (Wed Nov 06 19:01:20 GMT 2024) ----- HST Phase I Proposal 5957 successfully submitted. Receipt: # 5957-2 ----- Attempting Submission 3 (Thu Nov 07 14:25:21 GMT 2024) ----- HST Phase I Proposal 5957 successfully submitted. Receipt: # 5957-3 STScI have flagged this program as unschedulable, although this was not apparent in the submitted phase II APT. This issue was only caught after the observing window last year was over and no data had been taken. After some investigation, Milo Docher and Joel Green believe the main problem is that the ORIENT (PA) constraints are too narrow, particularly given HST’s current single‑gyro operations, which severely restrict the available ORIENT ranges. To fix this I have increased the orientation angle tolerance by 1 on each end. That gives me a 32-day viability window which I hope will be sufficient.  A small change in orient leads to an orbit overrun, requiring a reduction in the exposure length for dither position 4 in each mosaic pointing. To accommodate this, I changed the setup of the diter posstion 12 from NSAMP=8 with SAM-SEQ=STEP200 to NSAMP=7 with SAM-SEQ=STEP100 to ensure it fits within one orbit. -520448103 ----- Attempting Submission 1 (Fri Jan 31 17:25:33 GMT 2025) ----- HST Phase II Proposal 17910 successfully submitted. Receipt: # 17910-1 ----- Attempting Submission 2 (Fri Jan 31 19:10:14 GMT 2025) ----- HST Phase II Proposal 17910 successfully submitted. Receipt: # 17910-2 ----- Attempting Submission 3 (Fri Jan 31 19:11:26 GMT 2025) ----- HST Phase II Proposal 17910 successfully submitted. Receipt: # 17910-3 ----- Attempting Submission 4 (Fri Jun 06 12:01:33 GMT 2025) ----- ----- Attempting Submission 5 (Mon Jan 12 13:15:10 GMT 2026) ----- Silicates vs Carbon dust in NGC 6822: determining stellar dust types with WFC3/IR's unique filters Asymptotic Giant Branch (AGB) stars are important drivers of the chemical enrichment of the interstellar medium (ISM) in galaxies. They can form carbonaceous and silicate dust at metallicities as low as 0.6% solar, and can potentially inject mass into the ISM of galaxies 30 Myr after they form. The two species (C- and M-type) are split by different dominant surface chemistry (carbon- and oxygen-rich respectively) which affects the dust grains formed, dust mass, opacity and mass-loss efficiency and in turn, causes them to evolve at different rates. Disentangling these two species is key to understanding the effects they have on their environment. JWST imaged the local dwarf galaxy NGC 6822 and identified ~1200 candidate AGB stars. However, it has been shown that JWST medium- and wide-band photometry is not effective at identifying the chemistry of these stars, especially in low metallicity environments. HST can rectify this. With WFC3/IR F127M, F139M and F153M imaging of the same area, we can reliably constrain the stellar chemistry for SED fitting using the broad baseline (1-21 micron) photometry from JWST. This ensures accurate dust mass and type measurements to assess the contribution that AGB stars have to the dust budget in the early Universe. In addition this will provide validation to the method of identifying AGB species with JWST SED models. Targets: We will target 6 fields in NGC6822 that overlaps with JWST GTO #1234 coverage. 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 Avoiding Saturation: There are ~10 known stars in the field-of-view that are brighter than Ko=13.5mag saturation limit of the longest exposure (199s). From the sample of >1millions stars, these sources will not affect the science of our program. Other bright stars in the field will be recovered by the WFC3/IR MULTIACCUM sampling. 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 while minimizing the time needed to release high-level data products. 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. Olivia Jones is a Webb fellow who is an expert on infrared imaging and spectroscopy of stars in the Local Volume. She is an expert in the analysis and interpretation of IR photometry of dusty and evolved stars in nearby dwarf galaxies. 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. Stellar Populations and the Interstellar Medium 6 false false false false false false false SUPPORTED GALAXY STAR FORMING REGION UNDESIGNATED This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/IR Imaging No No F127M WFC3/IR Imaging No No F139M WFC3/IR Imaging No No F153M Hst Same orient constraint links visits (01 02 03 04 05 06) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17910-v01.xml (Tic-Visit :proposal-id 17910 :visit-id "01" :proposal-version -1 :trans-version "20250929" :date "14-Jan-2026 12:00:16.0" :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 17910 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17910 :visit-id "01" :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 Hst Same orient constraint links visits (01 02 03 04 05 06) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17910-v02.xml (Tic-Visit :proposal-id 17910 :visit-id "02" :proposal-version -1 :trans-version "20250929" :date "14-Jan-2026 12:00:16.0" :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 17910 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17910 :visit-id "02" :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 Hst Same orient constraint links visits (01 02 03 04 05 06) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17910-v03.xml (Tic-Visit :proposal-id 17910 :visit-id "03" :proposal-version -1 :trans-version "20250929" :date "14-Jan-2026 12:00:17.0" :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 17910 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17910 :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 Hst Same orient constraint links visits (01 02 03 04 05 06) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17910-v04.xml (Tic-Visit :proposal-id 17910 :visit-id "04" :proposal-version -1 :trans-version "20250929" :date "14-Jan-2026 12:00:17.0" :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 17910 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17910 :visit-id "04" :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 Hst Same orient constraint links visits (01 02 03 04 05 06) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17910-v05.xml (Tic-Visit :proposal-id 17910 :visit-id "05" :proposal-version -1 :trans-version "20250929" :date "14-Jan-2026 12:00:18.0" :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 17910 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17910 :visit-id "05" :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 Hst Same orient constraint links visits (01 02 03 04 05 06) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17910-v06.xml (Tic-Visit :proposal-id 17910 :visit-id "06" :proposal-version -1 :trans-version "20250929" :date "14-Jan-2026 12:00:18.0" :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 17910 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17910 :visit-id "06" :orbit-number 1 :pcs-time 301 :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