0 Assigned ID: 1823 ----- Attempting Submission 1 (Fri Apr 09 04:58:10 GMT 2021) ----- INVALID GS ACQ SCENARIO SPECIAL REQUIREMENT INVALID GS ACQ SCENARIO SPECIAL REQUIREMENT INVALID GS ACQ SCENARIO SPECIAL REQUIREMENT INVALID GS ACQ SCENARIO SPECIAL REQUIREMENT INVALID GS ACQ SCENARIO SPECIAL REQUIREMENT INVALID GS ACQ SCENARIO SPECIAL REQUIREMENT To minimise systematics, our observations require the exact same field configurations (pointing, aperture, and telescope orientation) as the first-epoch observations. As discussed by email, the strict orientation constraints limit the available observing windows and it may be necessary to find a tradeoff between the available time per orbit (via the "schedulability" parameter) and the duration of the possible windows. Ideally the integration time per orbit should be kept as long as is practical. Update 28 January 2023: Added a duplicate of failed visit 09 for rescheduling (approved HOPR 92399) Update 13 February 2023: Adjusted the allowed ORIENT range for visit 11 (visit 09 repeat) to allow scheduling 1096040117 ----- Attempting Submission 1 (Fri Jul 23 01:38:55 GMT 2021) ----- ----- Attempting Submission 2 (Sat Jan 28 09:37:46 GMT 2023) ----- HST Phase II Proposal 16746 successfully submitted. Receipt: # 16746-2 ----- Attempting Submission 3 (Mon Feb 13 09:39:41 GMT 2023) ----- These errors are on already completed visits Reconstructing Andromeda's accretion history with remote globular clusters: a pilot proper motion study Resolved observations of the stellar halos of nearby galaxies yield critical insight into the mass assembly history in these systems, allowing the predictions of cosmological models to be directly confronted with experimental data. Andromeda (M31) is a key location for this endeavour, offering a second data point, and exhibiting strikingly different halo properties, to the Milky Way. Here we propose to take the first step towards obtaining full 6D orbital phase-space information for stellar substructures in the M31 halo, by undertaking a pilot survey to measure proper motions for a small set of globular clusters with first-epoch ACS/WFC imaging taken 11-17 years ago. By comparison with recent HST proper motion studies of larger stellar systems out to the distance of M31, we expect to achieve a precision of ~0.010-0.015 mas/yr with these baselines. This compares favourably with the observed 1D (line-of-sight) kinematics of M31's outer globular cluster system, which exhibit a velocity dispersion of ~100 km/s (0.027 mas/yr) plus coherent rotation of comparable amplitude. These pilot measurements will provide the first 6D phase-space information for any extragalactic stellar stream, and enable a new, independent estimate of the shape and mass of the M31 dark halo at very large radii (50-120 kpc). By demonstrating feasibility and optimising our methodology with this data set, we ultimately aim to extend similar measurements to a much larger cluster sample in future, facilitating detailed orbital modelling that will accurately reconstruct the main events in M31's accretion history. This is a pilot study aimed at measuring proper motions for five globular clusters in the halo of Andromeda (M31) using ACS/WFC. The first-epoch data were obtained in the programs listed below, between ~11-16 years ago. This program will obtain second-epoch data, and measure the motions of the stars in the clusters by comparing their change in positions relative to compact background galaxies. Of our five targets, PAndAS-02 was observed in program GO-12515; B514 was observed in programs GO-10394 and GO-10565; HEC12 was observed in program GO-10394; and PAndAS-53 and 54 were observed in program GO-12515 and share the same ACS/WFC field. As explained in our Phase I, most of the first-epoch imaging consists of 3 exposures in F606W and 3 exposures in F814W. We would like to use all of these images, to maximise the number of frames that can be used to estimate the proper motion. However none of the first-epoch data were designed for astrometry. We will use the second-epoch images from the present program to construct reference images in both F606W and F814W, with dithers, etc, optimised for astrometry. The exception to this is target B514, for which two sets of first-epoch data exist. For this target we will therefore obtain second-epoch imaging using only F606W, which provides the best astrometric handle on the background galaxies. To minimise systematics, our observations require the exact same field configurations (pointing, aperture, and telescope orientation) as the first-epoch observations. In particular, the strict orientation constraints limit the available observing windows and it may be necessary to find a tradeoff between the available time per orbit (via the "schedulability" parameter) and the duration of the possible observing windows. Observations for a given target and filter occupy one visit and are split into four long exposures (~1100-1200s each) over two orbits. Ideally these integrations need to be as long as possible to maximise the S/N for both faint stars and the background galaxies. We use customised dither patterns (via POS-TARGs) to optimise the pixel phase coverage (e.g., as in program GO-14734). We add one short (60s) exposure per visit to avoid saturating stars at V~17-18th magnitude that could be used to tie our astrometry to the Gaia reference frame in future. Dr Dougal Mackey (program PI) is an expert on HST observations of resolved stellar populations in the Local Group, with a particular focus on globular clusters. He has been the lead author of a dozen papers based on resolved HST photometry and astrometry of globular clusters in the Magellanic Clouds, other Local Group dwarf galaxies, and the M31 halo. He is the PI of HST programs GO-12515, 13374, and 13375, which comprise much of the first-epoch imaging off which the present proposal is based. Prof Annette Ferguson also has extensive experience with HST observations of resolved stellar populations, with a particular focus on the M31 disk and halo, where her team has undertaken wide-ranging analysis of metallicity distributions and star formation histories. Prof Geraint Lewis, Prof Rodrigo Ibata, and Dr Nicolas Martin are experts on the M31 halo and, together with Mackey and Ferguson, formed a key portion of the Pan-Andromeda Archaeological Survey (PAndAS) team. Lewis and Ibata have lengthy experience with modelling stellar streams in galaxy halos, which is a key motivation for undertaking the present program. Dr Avon Huxor is an expert on the globular cluster system of M31, and within PAndAS was responsible for the discovery of nearly 100 new outer halo members. Graduate students Patricio Amaro and Lara Cullinane are, respectively, experts on HST photometry of Local Group clusters, and the internal kinematics of Local Group galaxies. Stellar Populations and the Interstellar Medium 6 false false false false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER First epoch from GO-12515, 3x F606W and 3x F814W. Aperture WFC1. Line dither. Central point of dither at 359.4809683683 +41.78042220476 with PA_V3 = 278.927. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER First epoch from GO-10394, 3x F606W. Aperture WFC1. Line dither. Central point of dither at 7.791116850289 +37.90020898981 with PA_V3 = 60.533. First epoch from GO-10565, 3x F606W. Aperture WFC1. Line dither. Central point of dither at 7.791007884871 +37.89992743316 with PA_V3 = 81.922. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER First epoch from GO-10396, 3x F606W and 4x F814W. Aperture WFC1. Line dither. Central point of dither at 14.56429054236 +38.04454067485 with PA_V3 = 63.769. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER First epoch from GO-12515, 3x F606W and 3x F814W. Aperture WFCENTER. Line dither. Central point of dither at 19.49624159651 +39.2662330971 with PA_V3 = 331.271. J2000 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W The scheduling data was generated by CASM 30.3. CASM was run in Phase II mode. 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