0 Assigned ID: 4270 ----- Attempting Submission 1 (Wed May 24 06:45:17 GMT 2023) ----- HST Phase I Proposal 4270 successfully submitted. Receipt: # 4270-1 ----- Attempting Submission 2 (Wed May 24 19:22:56 GMT 2023) ----- HST Phase I Proposal 4270 successfully submitted. Receipt: # 4270-2 ----- Attempting Submission 3 (Wed May 24 20:37:21 GMT 2023) ----- The number of orbits used exceeds the number allocated ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN To whom it may concern, This is a resubmission of my Cycle 31 proposal, since a accumulated of 3 orbits failed. See the TTRB approval below. You submitted HOPR 93468 for HST program 17438 on February 02, 2026. After review, the Telescope Time Review Board (TTRB) approves your request and awards two orbits to repeat the observations in Visit 07, which suffered guide-star acquisition and tracking anomalies, leading to degraded data. Additionally, the TTRB awards one orbit to recover the failed observations in Visits 05 and 06, which suffered guide-star acquisition anomalies. We also approve your request to execute the repeats at the SAME ORIENT as the successful observations. Please note that the scheduling of the repeats will be handled on a best effort basis only. The request is within the 90-day limit, and the program is less than 90% complete. The failed data from Visit 07 will be made public immediately. Claus Leitherer, head of the Science Policies Group, has concurred in our recommendation. Best, Maude -1029413926 ----- Attempting Submission 1 (Mon Sep 11 07:03:39 GMT 2023) ----- ----- Attempting Submission 2 (Thu Jan 11 09:55:47 GMT 2024) ----- ----- Attempting Submission 3 (Thu Mar 27 21:56:37 GMT 2025) ----- ----- Attempting Submission 4 (Mon Feb 09 18:22:25 GMT 2026) ----- A warning is raised for number of orbits, but was approved for 3 new orbits (see HOPR approval). Remaining warnings concern previous orbits, not the new observations, hence ignored. Emission-line stars in the extremely metal-poor dwarf galaxy Sextans A We propose HST/ACS Halpha (F658N) imaging to build the largest uniform sample of emission-line stars at sub-SMC metallicity by targeting the dwarf galaxy Sextans A. We will identify and characterize ~500 emission-line stars (Be, Oe, etc) at Z~0.1 Zsun, a >10x increase in the number of emission-line stars known at this metallicity. Such emission-line stars are expected to be a common phase of evolution for intermediate mass and massive stars, particularly at the low-metallicities, but there are few data points available to constrain theoretical predictions (fraction of emission-line stars, relationship to age, etc). Our large, homogenous study of these emission-line stars will greatly improve our knowledge of massive star evolution at low-metallicities as a function of age, metallicity, and location on the HR diagram. We will also supply the first constraints on the emission-line star contamination fraction of intermediate mass core blue helium burning stars (BHeBs; Mstar >~2 Msun) at such low metallicities. BHeBs provide critical tests for the physics of the post-main sequence stellar evolution (e.g., mass loss, rotation). This program will provide essential data to the broader community interested in other emission line stars such as symbiotic stars, PNe, luminous M(e) stars, massive young stellar objects, and binary-stripped stars. Observations of such low-metallicity emission line stars can only be made with HST, as they are all too faint and crowded for spectroscopic or ground-based imaging studies. This program will obtain precise F658N ACS photometry of Sextans A and matched F625W imaging.The goal is to obtain all O and B type stars in the field down to F475W ~ 25.5 mag in order to have a complete stellar population study of the emission line phenomena at low metallicity. Furthermore we are also investigating the emission-line star contamination fraction of intermediate mass core blue helium burning stars. In total we have 4 visits planned. The first 3 visits will each consist of 2 orbits acquiring 8 F658N exposures over a 4-point box dither pattern with sub-pixel spacing. The exposure times have been optimized to maximize the SNR. The last visit will consist of 2 orbits where we will acquire 4 F658N exposures and 4 F625W exposures. The exposures in each filter will be taken consecutively of each pointing before moving to the next pointing in a 4-point box dither pattern. This combination was done to maximize F658N exposures, while simultaneously avoiding the dump buffer time of short exposures taking up exposure time. We have specified ORIENTS of 55-65 degrees and 319 degrees, which are all acceptable for our science goals. We require SAME ORIENT for each visit to maximize the SNR of the stars in our sample, and ensure that we reach the necessary depth of the stars in our field. We expect minimal impact from Reduced Gyro Mode (RGM). Our team includes members of multiple HST Treasury, large GO, and Archival programs of resolved stellar populations in the Local Group and Volume (e.g., PHAT, LUVIT, ANGST, ANGRRR, ANGST-SNAP, GHOSTS). We have observed, reduced, analyzed, and disseminated >1500 orbits of HST imaging, resulting in publicly released photometry in excess of 100 million stars. 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 Gull is an expert in massive stars and metal-poor stars. Co-I Weisz is an expert in stellar populations studies and the local group galaxies. Co-I Boyer is an expert in evolved stars and their impact on their host galaxy. Co-I Choi is an expert in galaxy evolution and stellar population interactions with the ISM . Co-I Dalcanton is an expert in space-based photometric survey and galaxy evolution. Co-I Durbin is an expert on space-based photometry. Co-I El-Badry is an expert in binary stars and Be stars. Co-I Gilbert is an expert in resolved stellar population studies and star formation histories. Co-I McLeod is an expert in stellar feedback, and massive stars. Co-I Savino is an expert in resolved stellar populations in the Local Volume and stellar ages. Co-I Sandford is an expert in resolved stellar populations and low-metallicity stellar spectrooscopy. Co-I Skillman is an expert in dwarf galaxies and resolved stellar populations. Gull will lead the data processing, SED analysis with the BEAST tool with input from co-Is Weisz and Choi. The BEAST is publicly available and ready for use - our team continuously improves on its capabilities (Choi). Photometry, images, and SED fits will be released via a database interface developed for PHAT. Stellar Populations and the Interstellar Medium 6 false false false false false false false SUPPORTED GALAXY STAR FORMING REGION This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 ACS/WFC Imaging No No F658N ACS/WFC Imaging No No F625W POS-TARG DITHER 0.2637 LINE 0.1856 false false 69.02 4 20.7 ACS-WFC-DITHER-BOX 1 false /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17438-v01.xml Hst Same orient constraint links visits (01 02 03 04 10) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 1738664138000 319.0 (Tic-Visit :proposal-id 17438 :visit-id "01" :proposal-version -1 :trans-version "20250929" :date "13-Feb-2026 12:11:08.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2622 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2624 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 2 Hst Same orient constraint links visits (01 02 03 04 10) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 1738760499000 319.0 (Tic-Visit :proposal-id 17438 :visit-id "02" :proposal-version -1 :trans-version "20250929" :date "09-Feb-2026 12:08:54.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2622 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2624 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 2 /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17438-v03.xml Hst Same orient constraint links visits (01 02 03 04 10) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 1738856889000 319.0 (Tic-Visit :proposal-id 17438 :visit-id "03" :proposal-version -1 :trans-version "20250929" :date "13-Feb-2026 12:01:42.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2622 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "03" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2624 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 2 /System/Volumes/Data/solaris/user1/mdocher/hst-work/OP-cache/17438-v10.xml Hst Same orient constraint links visits (01 02 03 04 10) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17438 :visit-id "10" :proposal-version -1 :trans-version "20250929" :date "13-Feb-2026 12:10:27.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "10" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 Hst Same orient constraint links visits (01 02 03 04 10) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 1738749159000 319.0 (Tic-Visit :proposal-id 17438 :visit-id "04" :proposal-version -1 :trans-version "20250929" :date "09-Feb-2026 12:09:03.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2625 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "04" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2625 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 2 Hst Same orient constraint links visits (05 06 07 09) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 1768986092000 319.0 (Tic-Visit :proposal-id 17438 :visit-id "05" :proposal-version -1 :trans-version "20250929" :date "09-Feb-2026 12:09:05.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2622 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "05" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2624 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 2 Hst Same orient constraint links visits (05 06 07 09) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 1769070693000 319.0 (Tic-Visit :proposal-id 17438 :visit-id "06" :proposal-version -1 :trans-version "20250929" :date "09-Feb-2026 12:09:09.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2622 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "06" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2624 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 2 Hst Same orient constraint links visits (05 06 07 09) The scheduling data was generated by CASM 34.0. CASM was run in Phase II mode. 1769877827000 319.0 (Tic-Visit :proposal-id 17438 :visit-id "07" :proposal-version -1 :trans-version "20250929" :date "09-Feb-2026 12:09:12.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "07" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2625 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "07" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2625 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 2 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/17438-v08.xml (Tic-Visit :proposal-id 17438 :visit-id "08" :proposal-version -1 :trans-version "20250929" :date "11-Feb-2026 14:39:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1136896 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "08" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 Hst Same orient constraint links visits (05 06 07 09) 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/17438-v09.xml (Tic-Visit :proposal-id 17438 :visit-id "09" :proposal-version -1 :trans-version "20250929" :date "11-Feb-2026 14:39:51.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17438 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17438 :visit-id "09" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17438 :visit-id "09" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2599 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0