0 Assigned ID: 2870 ----- Attempting Submission 1 (Wed Mar 23 13:38:06 GMT 2022) ----- HST proper-motion determinations of the Milky Way's dwarf galaxies have proven to be extremely useful in understanding our own Galaxy and the 3D dynamics of its satellite system. We propose to extend the astrometric reach of HST to the satellite system of the Andromeda galaxy. Specifically, we propose to measure the absolute proper motions of six satellites of the Andromeda galaxy using existing, archived exposures that span ~20 years. Such an unprecedented HST time baseline is achieved by combining images taken with WFPC2 and ACS/WFC. To realize the full potential of these data we will take advantage of a recently completed astrometric re-calibration of WFPC2 as well as the most recent updates to the ACS/WFC calibration. The expected accuracy of each satellite's tangential velocity is 40 km/s. Upon completion of the project, our sample will double the number of Andromeda satellites with well-measured proper motions, once these are added to the results of a separate (currently active) HST observing proposal. We will also analyze the orbital information provided by the sample of Andromeda satellites with known 3D velocities, as this sample grows. Andromeda represents the only feasible opportunity for obtaining 3D velocities and performing such a study for a system beyond that of our own Milky Way. We will directly test very specific models for the formation of the Great Plane of Andromeda. We will also compare satellite orbit statistics of the Andromeda and the Milky Way systems in an effort to understand puzzling observational aspects that are not seen in state-of-the-art cosmological models. PI Dana I. Casetti: She has over 25 years of experience as a research scientist in Galactic structure and kinematics. Responsible for measuring and compiling the most comprehensive, pre-Gaia catalog of absolute proper motions of globular clusters (with ~20 citations/year for 15 years), as well as the for measuring the first absolute proper motions in distant tidal streams and halo overdensities. Expertise in astrometry with photographic plates and large format CCDs (including SuprimeCam on Subaru). PI on HST AR proposal 15632, "Expanding HST's Astrometry Legacy: A Comprehensive Astrometric Calibration of WFPC2" which has produced improved distortion correction maps for this camera in three filters. An immediate outcome of this calibration is the new determination of Leo I proper motion, now a member of the polar alignment of Milky-Way satellite galaxies. Co-I Terrence M. Girard: He has over 35 years experience in astronomy research including astrometry, relative and absolute proper-motion studies, and astrometric calibration of imagers. He has constructed data analysis pipelines for several major research projects, including the Yale/San Juan Southern Proper Motion program and the Solar Disk Sextant. Responsible for the construction of the largest (area and depth), most accurate, pre-Gaia astrometric catalog, the Southern Proper-Motion Catalog 4. Responsible for developing code and methodology for calibrating the WFPC2 camera (Co-I on HST AR 15632). Girard also worked recently on a project to recalibrate and reprocess the La Silla-QUEST Southern Hemisphere Supernova and Variability Surveys. These surveys employed the 10-square-degree QUEST camera (112 detectors, each 2400x600 pixels) at the prime focus of the 1.0-m ESO Schmidt Telescope at La Silla, Chile. Girard reworked and streamlined the reduction pipeline at Yale, incorporating the Gaia EDR3 for astrometric and photometric calibration, thus greatly improving the astrometric output products, in particular. This work also gave benefit to an ongoing project at Yale to do a full-survey coadd of the hundreds of repeated QUEST exposures over the entire southern sky. Co-I Kosuke Kanehisa He is a PhD student at AIP in Dr. Pawlowski's group, working on the detailed comparison of observed planes of satellite galaxies with a range of cosmological simulations. He has experiences investigating satellite galaxy planes beyond the Milky Way, and has worked on the Centaurus A and M31 satellite systems. He is also experienced in predicting proper motions based on satellite galaxy plane geometry, orbit integrations of satellite galaxies, and properties of the host galaxy potential. Co-I Vera Kozhurina-Platais She is an expert in developing calibration procedures for the imaging cameras on board HST: WFPC2, ACS/WFC and WFC3/UVIS and IR. Her responsibilities as Principal Instruments Scientist at STScI are related to multi-wavelength astrometric calibration of these 4 cameras for the Calibration Data Base System to be used in the HST pipeline. She is also expert in working with the severely under-sampled HST point-spread-function (PSF) which is instrumental in astrometric studies. Co-I Marcel Pawlowski He is a junior research group leader at AIP and an expert in the investigation and interpretation of systems of satellite galaxies and their phase-space distribution, ranging from the Milky Way to more distant hosts, within the context of predictions from cosmological models. He works on small-scale problems of the LCDM model, and has in particular lead numerous studies on the planes of satellite galaxies problem of cosmology as well as the first invited review article on the issue. His research involves both observational data and cosmological simulation outputs, in order to obtain accurate measures of the agreement or tension between observed satellite galaxy structures and model expectations. He has also contributed to, and is currently involved in, several projects measuring and interpreting proper motions of nearby dwarf galaxies with both HST and Gaia. Co-I Imants Platais He has extensive expertise in astrometric studies (over 35 years) using ground and space-based observations. He has hands-on experience with the Large Magellanic Clouds images obtained with WFPC2, ACS/WFC, and WFC3/UVIS in the context of proper motions for potential runaway stars. He is the PI on the GO-15317 project which addresses photometry and absolute proper motions in a dwarf galaxy, and of AR-16629 which involves measuring astrometric acceleration in globular cluster omega Centauri (NGC 5139). Galaxies Stellar Populations and the Interstellar Medium 0 Regular false false false false false false SUPPORTED