18407( 2) - 13-Aug-2026 16:26:52 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18407 Version: 2 Check-in Time: 13-Aug-2026 16:26:52 STScI Edit Number: 0 Title New isolated, faint dwarf galaxies beyond the Local Group ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Burcin Mutlu-Pakdil Dartmouth College Y CoI: Prof. David J. Sand University of Arizona N CoI: Dr. Denija Crnojevic University of Tampa N CoI: Prof. Dennis Zaritsky University of Arizona N CoI: Dr. Paul Bennet Space Telescope Science Institute N CoI: Dr. Amandine Doliva-Dolinsky University of Surrey N CoI: Dr. Jeff Carlin NOIRLab - Vera C. Rubin Operations (AZ) N CoI: Dr. Laura Congreve Hunter Dartmouth College N CoI: Dr. Michael Gordon Jones California Institute of Technology N CoI: Dr. Jaclyn Jensen Dartmouth College N CoI: Dr. Kristine Spekkens Queen's University N CoI: Guinevere Herron Dartmouth College N CoI: Ms. Sasha N Campana Dartmouth College N CoI: Dr. Deepthi S. Prabhu University of Arizona N ------------------------------------------------------------------------------------ Abstract The Local Group satellite dwarf galaxies are often used as benchmarks for testing galaxy formation and evolution theories on the smallest scales because they are the lowest-mass galaxies for which detailed observations are available. However, most of these dwarfs have been affected by the Local Group environment. If we want to understand the physical mechanisms driving the evolution of low-mass galaxies, we must study dwarf galaxies beyond the Local Group across all environments. We request 8 orbits of ACS imaging (F606W+F814W) to follow up eight new nearby faint dwarf galaxies discovered in ground-based surveys. The galaxies are likely just beyond the edge of the Local Group. HST imaging is essential to the determination of high-precision distances, basic physical properties, and the star formation histories of these newly discovered faint dwarfs. The requested observations will put these eight galaxies into context with other dwarf galaxies in and beyond the Local Group, providing a rare opportunity to assess the impact of environment on low-mass systems. ------------------------------------------------------------------------------------ Observations Description ------------------------ The observations are going to be performed with ACS/WFC to match previous observations of faint dwarfs beyond the Local Group (e.g. Weisz et al. 2014, Hargis et al. 2020, Danieli et al. 2017, Bennet et al. 2019, Crnojevic et al. 2019, Mutlu-Pakdil et al 2022). We request imaging in F606W and F814W filters (broad V and I) for both instruments, in order to compute accurate TRGB distances for our targets and characterize their stellar content, while optimizing the exposure times. 18407( 2) - 13-Aug-2026 16:26:52 - [ 2] Given the small size of each target (<1 arcmin), one pointing is sufficient to cover the entire spatial extent of each galaxy. Each dwarf will be placed on one of the ACS/WFC chips, and small dithers between exposures will remove detector defects and improve the PSF sampling. Given that the possible distance range for our targets is ~1-3 Mpc, we use existing HST ACS data of Local Volume dwarfs at <3 Mpc (NGC253 dwarfs [GO-14259, GO-15938], CenA dwarfs [GO-13856], MADCASH dwarfs [GO-15228]) to guide our observational request and ensure that the depth is sufficient for the science goals of this proposal. The archival ACS data for similar limiting magnitudes were obtained with 2 CR-SPLIT exposures of 1200 sec in F606W and 900 sec in F814W. The required exposure times nicely fit into one orbit per object after taking into account realistic overheads. We have checked that the charge transfer efficiency losses of ACS do not significantly affect our observations (at most 10% loss of flux). Our visits are 1-orbit, and we have no ORIENT requirements. Nor does this program have time constraints (other than the baseline excitement of the science!) ------------------------------------------------------------------------------------ 18407( 2) - 13-Aug-2026 16:26:52 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG1 GALAXY, DWARF RA=12H39M2.5632S, J2000 V = 21 +/- 0.1 SPHEROIDAL DEC=-00D39'51.73" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG2 GALAXY, DWARF RA=10H40M10.1664S, J2000 V = 22 +/- 0.1 SPHEROIDAL DEC=+04D54'31.10" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 3 SMDG3 GALAXY, DWARF RA=01H11M51.9504S, J2000 V = 21 +/- 0.1 SPHEROIDAL DEC=+02D27'46.76" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 4 SMDG4 GALAXY, DWARF RA=13H00M59.7888S, J2000 V = 21 +/- 0.1 SPHEROIDAL DEC=-02D01'7.39" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 5 SMDG5 GALAXY, DWARF RA=11H06M7.5024S, J2000 V = 21 +/- 0.1 SPHEROIDAL DEC=-01D26'51.25" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 6 SMDG6 GALAXY, DWARF RA=12H45M52.3224S, J2000 V = 22 +/- 0.1 SPHEROIDAL DEC=+01D54'20.88" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 7 SMDG7 GALAXY, DWARF RA=12H38M50.0448S, J2000 V = 21 +/- 0.1 SPHEROIDAL DEC=-01D05'11.98" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 8 SMDG8 GALAXY, DWARF RA=12H21M32.7400S, J2000 V = 22 +/- 0.1 SPHEROIDAL DEC=+37D13'22.13" Reference Frame: ICRS Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 18407( 2) - 13-Aug-2026 16:26:52 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 3.034 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.29 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18407( 2) - 13-Aug-2026 16:26:52 - [ 5] Visit: 01 (SMDG1) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG1 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG1 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG1 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 479.0 S SMDG1 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 479.0 S SMDG1 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 479.0 S SMDG1 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 479.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 6] Visit: 02 (SMDG2) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG2 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG2 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG2 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 479.0 S SMDG2 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 479.0 S SMDG2 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 479.0 S SMDG2 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 479.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 7] Visit: 03 (SMDG3) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG3 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG3 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG3 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 479.0 S SMDG3 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 479.0 S SMDG3 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 479.0 S SMDG3 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 479.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 8] Visit: 04 (SMDG4) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG4 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG4 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG4 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 479.0 S SMDG4 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 479.0 S SMDG4 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 479.0 S SMDG4 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 479.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 9] Visit: 05 (SMDG5) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG5 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG5 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG5 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 479.0 S SMDG5 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 479.0 S SMDG5 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 479.0 S SMDG5 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 479.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 10] Visit: 06 (SMDG6) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG6 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG6 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG6 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 479.0 S SMDG6 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 479.0 S SMDG6 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 479.0 S SMDG6 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 479.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 11] Visit: 07 (SMDG7) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG7 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG7 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (958 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG7 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 479.0 S SMDG7 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 479.0 S SMDG7 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 479.0 S SMDG7 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 479.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 12] Visit: 08 (SMDG8) Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SMDG8 ACS/WFC ACCUM WFC1 F606W 1 400 S PATTERN 1 1 see below (964 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SMDG8 ACS/WFC ACCUM WFC1 F814W 1 400 S PATTERN 1 2 see below (964 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ SMDG8 1 ACS/WFC ACCUM WFC1 F606W 1 none none none 1 482.0 S SMDG8 1 ACS/WFC ACCUM WFC1 F606W 2 none none none 1 482.0 S SMDG8 2 ACS/WFC ACCUM WFC1 F814W 1 none none none 1 482.0 S SMDG8 2 ACS/WFC ACCUM WFC1 F814W 2 none none none 1 482.0 S 18407( 2) - 13-Aug-2026 16:26:52 - [ 13] Summary Form for Proposal 18407 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names SMDG1, SMDG2, SMDG3, SMDG4, SMDG5, SMDG6, SMDG7, SMDG8 ------------------------------------------------------------------------------------------------------------------------------------