0 Assigned ID: 2001 ----- Attempting Submission 1 (Fri Apr 09 16:15:07 GMT 2021) ----- HST Phase I Proposal 2001 successfully submitted. Receipt: # 2001-1 ----- Attempting Submission 2 (Fri Apr 09 17:54:29 GMT 2021) ----- HST Phase I Proposal 2001 successfully submitted. Receipt: # 2001-2 ----- Attempting Submission 3 (Fri Apr 09 17:55:38 GMT 2021) ----- HST Phase I Proposal 2001 successfully submitted. Receipt: # 2001-3 ----- Attempting Submission 4 (Fri Apr 09 18:38:40 GMT 2021) ----- The survival of widely separated binary stars within dense, low-mass dwarf galaxies depends strongly on the nature of dark matter. The standard Cold Dark Matter (CDM) model generically predicts that dwarf galaxy dark matter halos are composed of a smooth component with a centrally-divergent density "cusp", plus multitudes of self-bound subhalos, sub-subhalos, etc., down to a mass limit set by particle physics. Both smooth and clumpy components would disrupt wide binary stars, via tidal forces and perturbative encounters, respectively, leaving an imprint on the binary separation function. We propose to apply a novel, likelihood-based analysis to detect and characterize wide binary stars (separation > 3000 A.U.) in the nearby dwarf spheroidal galaxy Ursa Minor, which was observed for this purpose in Cycle 21 (GO-13470). We will apply Bayesian techniques to detect binary stars in a probabilistic sense. Improving on standard methodology that models the two-point correlation function, we will infer the binary separation function directly from the full distribution of stellar positions and known sensitivity function. We will interpret the results in the context of wide binary formation and survival in a dense dark matter halo environment, thereby providing novel tests of star formation in extreme environments and--especially if wide binaries are detected--a potentially definitive test of the CDM paradigm. P.I. Walker is Associate professor of Physics at Carnegie Mellon University. Walker has expertise in spectroscopic and photometric observations, statistical and dynamical modeling of dwarf galaxies-- particularly the faint satellites of the Milky Way. Walker's research aims primarily to infer the structure of dark matter halos on small scales, with the goal of contributing to an understanding of the microscopic nature of dark matter. Walker advises the Ph.D. student (Co-I Kervick), who will perform the statistical analysis of wide binary separation functions proposed here. Co-I Penarrubia is Professor and Chair of Gravitational Dynamics in the School of Physics and Astronomy, University of Edinburgh (UK). Penarrubia has expertise in numerical simulations and dynamical modeling of Milky Way satellites, with focus on tidally disrupting systems. His N-body simulations of the formation and destruction of wide binary systems within dwarf galaxies provide the theoretical underpinning of the work proposed here. For this project, Penarrubia will use results from our measurements to tailor N-body simulations to the Ursa Minor dwarf galaxy, aiming to find the combination of smooth halo substructure and substructure that account for the observed stellar population and its wide binary separation function. Co-I Kervick is a 5th-year Ph.D. student at Carnegie Mellon, working under the supervision of PI Walker. Kervick has generated the mock data sets used to gauge detectability wide binaries and reliability of our analysis, and has developed the statistical methodology that will be used to analyze wide binary stars for this program. Kervick will perform this analysis as part of the Ph.D. thesis. Stellar Populations and the Interstellar Medium Galaxies 0 Regular false false false false false SUPPORTED