0 Assigned ID: 352 ----- Attempting Submission 1 (Fri Apr 08 02:10:21 GMT 2016) ----- HST Phase I Proposal 352 (NGC147185.apt) successfully submitted. Receipt: # 352-1 ----- Attempting Submission 2 (Fri Apr 08 16:51:22 GMT 2016) ----- Resubmitted after making minor changes. First submission had some unused visibility, and in this resubmission, unused visibilities are all zero now. -666515056 ----- Attempting Submission 1 (Wed Jul 13 01:32:16 GMT 2016) ----- ----- Attempting Submission 2 (Fri Jul 15 15:10:54 GMT 2016) ----- Proper Motions of Two Local Prototype Dwarf Elliptical Galaxies NGC 147 and NGC 185 The factors governing the quenching of dwarf galaxies are of great importance to understanding galaxy formation. Deep HST photometry shows a significant difference in the quenching times between the otherwise seemingly similar dwarf elliptical galaxies NGC 147 and 185 in the halo of M31. The two galaxies are found close together on the sky with similar line-of-sight velocities, suggestive of a shared history. Measuring proper motions (PMs) of these two systems to constrain their orbits will allow us to differentiate between various quenching scenarios. We propose to target the same fields as the earlier deep HST observations, using the same instruments and orientations. For each galaxy, both the primary ACS and the parallel WFC3 fields will be used for PM measurments. We will use the same advanced techniques that allowed us to measure the PMs of M31 and Leo I. Thanks to the time baseline of 8 years, we expect to obtain one-dimensional PM accuracy of 25 km/s, far smaller than the velocity dispersion in the M31 halo. PM results will show whether these galaxies share a common dynamical history. We will convert the orbital energy of each galaxy to infall time, using correlations found in cosmological simulations. We will also compute orbits for both galaxies to find their pericenters as they orbit M31 and relate those to their tidal distortions, stellar streams, and differing gas content. Both galaxies also belong to M31's surprising "plane of satellites", and the PMs we obtain will test the nature of this plane. Together, these results will isolate the factors responsible for their differing quenching times. These will be the first PM measurements for dwarf galaxies of M31. To measure absolute proper motions of NGC 147/185, 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 the first and second epoch with respect to these reference sources. Our analysis techniques and expected accuracies are described in the Phase I proposal. First epoch ACS/WFC and WFC3/UVIS data are available as part of previous HST program GO-11724 (PI: M. Geha). The present program will obtain second-epoch data. The first-epoch ACS/WFC and WFC3/UVIS data were obatined using two filters (F606W and F814W) to make deep color magnitude diagrams that reach a few magnitudes below the main sequence turnoff of NGC 147/185. The available broad-band colors and depth are sufficient for separating member stars of these target galaxies, foreground stars, and background galaxies to first order. For the second epoch, it is therefore necessary to take data in only one of the filters. Our past experience shows that F606W provides the best astrometric handle on background galaxies so that will be the filter of our choice. We will observe NGC 147/185 using the exact same field configurations (telescope pointings and orientations) as the first-epoch observations to maximize the overlaps of both the primary ACS/WFC and parallel WFC3/UVIS fields between the first- and second-epoch data. Individual exposures will be sub-pixel dithered and will last half an orbit. We will use customized dither patterns (via POS-TARG parameters) to maximize the pixel phase coverage. Stellar Populations Galaxies 12 false false false false false false SUPPORTED GALAXY DWARF ELLIPTICAL HALO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY DWARF ELLIPTICAL HALO This object was generated by the targetselector and retrieved from the SIMBAD database. 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 /private/var/folders/00/sjldtf2n1sg4dwsvr2x2ns340000gn/T/OPVisit2730295385674181895.xml Timing link suitability includes constraints ([Group (01 02) Within 15.0 days]) The scheduling data was generated by CASM 24.2. CASM was run in Phase II mode. This is the first visit for obtaining second-epoch images of NGC 147. This visit spends 2 orbits in total with ACS/WFC being the primary and WFC3/UVIS being the pallalel instruments. For proper motion purpose, we require to match our telescope positions and orientations to the first-epoch observations. We have accordingly added the Visit Orientation Requirements. We have grouped Visits 01 and 02 and specified these to visits to be observed within a 15 day period so that all images of NGC 147 can be treated as a single-epoch data for astrometric analysis. 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CASM was run in Phase II mode. This is the second visit for obtaining second-epoch images of NGC 147. This visit spends 2 orbits in total with ACS/WFC being the primary and WFC3/UVIS being the pallalel instruments. For proper motion purpose, we require to match our telescope positions and orientations to the first-epoch observations. We have accordingly added the Visit Orientation Requirements. We have grouped Visits 01 and 02 and specified these to visits to be observed within a 15 day period so that all images of NGC 147 can be treated as a single-epoch data for astrometric analysis. 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CASM was run in Phase II mode. This is the first visit for obtaining second-epoch images of NGC 185. This visit spends 2 orbits in total with ACS/WFC being the primary and WFC3/UVIS being the pallalel instruments. For proper motion purpose, we require to match our telescope positions and orientations to the first-epoch observations. We have accordingly added the Visit Orientation Requirements. We have grouped Visits 03 and 04 and specified these to visits to be observed within a 15 day period so that all images of NGC 185 can be treated as a single-epoch data for astrometric analysis. 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CASM was run in Phase II mode. This is the second visit for obtaining second-epoch images of NGC 185. This visit spends 2 orbits in total with ACS/WFC being the primary and WFC3/UVIS being the pallalel instruments. For proper motion purpose, we require to match our telescope positions and orientations to the first-epoch observations. We have accordingly added the Visit Orientation Requirements. We have grouped Visits 03 and 04 and specified these to visits to be observed within a 15 day period so that all images of NGC 185 can be treated as a single-epoch data for astrometric analysis. 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