0 Assigned ID: 950 ----- Attempting Submission 1 (Fri Apr 10 22:28:41 GMT 2015) ----- HST Phase I Proposal 950 (UFD.apt) successfully submitted. Receipt: # 950-1 ----- Attempting Submission 2 (Fri Apr 10 23:44:49 GMT 2015) ----- HST Phase I Proposal 950 (UFD.apt) successfully submitted. Receipt: # 950-2 ----- Attempting Submission 3 (Fri Apr 10 23:46:09 GMT 2015) ----- 0 ----- Attempting Submission 1 (Tue Jul 21 17:29:19 GMT 2015) ----- The First Proper Motions of Ultra-faint Dwarf Galaxies: Probing Reionization and Planar Associations of Satellites Ultra-faint dwarf (UFDs) galaxies are the least luminous, dark-matter dominated galaxies in our Universe. As potential fossil relics of the epoch of reionization, these extreme galaxies play a crucial role in reconciling predictions from LCDM theory, such as the observed number of satellites about our Milky Way (MW). However, none of these galaxies have measured proper motions (PMs), meaning we do not know their orbital histories or their relationship to other satellites over time. We propose to use HST ACS/WFC to make the first PM measurements for 6 UFDs with star formation histories suggesting quenching at the epoch of reionization. Using techniques we have developed to model the orbits of satellites like Leo I and the Magellanic Clouds, these PMs will constrain the orbital histories of a representative sample of UFDs for the first time. We will furthermore compare these orbits to predictions for UFDs from cosmological simulations made by our team. HST is significantly more accurate for PM measurements of our target galaxies than Gaia. Moreover, with HST we can do these measurements now, whereas the most accurate Gaia measurements are still 7 years into the future. With only a modest investment of HST time and proven techniques of our team, these novel HST observations will thus revolutionize our understanding of UFDs, establishing for the first time: (1) Whether star formation was suppressed by reionization; (2) Whether the UFDs ever passed close enough to the MW to have undergone significant tidal heating; and (3) Whether the UFDs orbit in a plane that is associated with the classical satellites. To measure absolute proper motions of our 4 target galaxies, we will use compact background galaxies in the field of view (FOV) as stationary reference sources. We will measure the average motion of stars in the target galaxies between epochs 1 and 2 with respect to these reference sources. Our analysis techniques and expected accuracies are described in the Phase I proposal. First epoch ACS data are available as part of previous observing programs by PI T. Brown (Proposal GO-12549). The present project will obtain the second epoch data. The first epoch ACS data were obtained in two filters (F606W and F814W) to make deep color magnitude diagrams that reach well below the main sequence turn-off of our target galaxies. The available broad-band colors and depth are sufficient for separating dwarf member stars, foreground stars, and background galaxies to first order. For the second epoch it is therefore sufficient to take data in only one of the filters. We will observe the target galaxies with the F606W filter using the same pointing and orientation used for the first epoch data. Individual exposures will be sub-pixel dithered and will last one-third to half an orbit. We will use customized dither patterns to maximize the pixel phase coverage. To maximize the time baseline, we have added Timing Requirements for 3 of our visits. During our second epoch observations, the WFC3/UVIS camera will be pointed ~6 arcmin away in the outer halo of each target galaxy. These parallel fields overlap with the first-epoch images as well, but the expected stellar density is much lower than the ACS/WFC fields. Nevertheless, we will identify dwarf member stars and measure their proper motions using the same measurement technique as we use for the ACS/WFC data. These will further reduce our final proper motion errors. RESOLVED STELLAR POPULATIONS 12 false false false false SUPPORTED GALAXY DWARF SPHEROIDAL J2000 J2000 GALAXY DWARF SPHEROIDAL J2000 J2000 GALAXY DWARF SPHEROIDAL J2000 J2000 GALAXY DWARF SPHEROIDAL J2000 J2000 ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F606W /Users/tsohn/Dropbox/HST Phase II/PID14236-UFDs/OP-cache/PID14236-v01.xml The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. This visit is for obtaining second-epoch images of the Canes Venatici II dwarf spheroidal galaxy. Four orbits are required to complete this visit. Since our goal is to measure proper motions of stars in our target galaxies, our orientation is set to exactly match the first-epoch images of GO-12549. We adopt a customized dither pattern to optimally cover the pixel phase using the POS-TARG requirements. (Tic-Visit :proposal-id 14236 :visit-id "01" :proposal-version -1 :trans-version "20150609" :date "15-Jul-2015 11:24:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 4583744 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14236 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14236 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2912 :al-overhead-at-end 70 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14236 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3022 :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 3245 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14236 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3022 :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 3245 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14236 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3022 :al-overhead-at-end 0 :internal-dur-at-end 1015 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3245 :pcs-gap 0 ) true 4 0 /Users/tsohn/Dropbox/HST Phase II/PID14236-UFDs/OP-cache/PID14236-v02.xml The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. This visit is for obtaining second-epoch images of the Hercules dwarf spheroidal galaxy. Three orbits are required to complete this visit. Since our goal is to measure proper motions of stars in our target galaxies, our orientation is set to exactly match the first-epoch images of GO-12549. We adopt a customized dither pattern to optimally cover the pixel phase using the POS-TARG requirements. The Visit Planner shows that our observations for this visit are available during two separate windows: one in Aug 2015 and the other in Aug 2016. It is necessary to maximize the time baseline of our proper motion measurements to fulfill our scientific goals, se we request this visit to be taken in Aug 2016. For this, we have added the Timing Requirements. 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CASM was run in Phase II mode. This visit is for obtaining second-epoch images of the Leo IV dwarf spheroidal galaxy. Four orbits are required to complete this visit. Since our goal is to measure proper motions of stars in our target galaxies, our orientation is set to exactly match the first-epoch images of GO-12549. We adopt a customized dither pattern to optimally cover the pixel phase using the POS-TARG requirements. We have found that the with the requested orientation and default Schedulabilty, The Visit Planner fails to find observable windows. Therefore, we increased the Schedulability to 40. Also, the Visit Planner shows that our observations for this visit are available during two separate windows: one in late 2015 to early 2016, and the other in late 2016 to early 2017. It is necessary to maximize the time baseline of our proper motion measurements to fulfill our scientific goals, se we request this visit to be taken in the latter window. For this, we have added the Timing Requirements. 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CASM was run in Phase II mode. This visit is for obtaining second-epoch images of the Hercules dwarf spheroidal galaxy. Three orbits are required to complete this visit. Since our goal is to measure proper motions of stars in our target galaxies, our orientation is set to exactly match the first-epoch images of GO-12549. We adopt a customized dither pattern to optimally cover the pixel phase using the POS-TARG requirements. The Visit Planner shows that our observations for this visit are available during two separate windows: one in Jan-Feb 2016 and the other in Jan-Feb 2017. It is necessary to maximize the time baseline of our proper motion measurements to fulfill our scientific goals, so we request this visit to be taken in Jan-Feb 2017. For this, we have added the Timing Requirements. 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