0 Assigned ID: 1150 ----- Attempting Submission 1 (Fri Apr 07 23:45:03 GMT 2017) ----- HST Phase I Proposal 1150 (streams.apt) successfully submitted. Receipt: # 1150-1 ----- Attempting Submission 2 (Fri Apr 07 23:54:45 GMT 2017) ----- HST Phase I Proposal 1150 (streams.apt) successfully submitted. Receipt: # 1150-2 ----- Attempting Submission 3 (Fri Apr 07 23:56:32 GMT 2017) ----- HST Phase I Proposal 1150 (streams.apt) successfully submitted. Receipt: # 1150-3 ----- Attempting Submission 4 (Sat Apr 08 00:06:06 GMT 2017) ----- HST Phase I Proposal 1150 (streams.apt) successfully submitted. Receipt: # 1150-4 ----- Attempting Submission 5 (Sat Apr 08 00:45:12 GMT 2017) ----- HST Proper Motion (PM) measurements over the past decade have revolutioned our understanding of Local Group Dynamics. This offers the opportunity to obtain crucial new constraints on the outer halo of the two main Local Group galaxies, the Milky Way and M31. These halos are crucial for understanding the growth of these galaxies, and the physics of the dwarf galaxy population around them. Yet their structures and gravitational potential are very poorly known. We propose to model recent HST PM data of the Sagittarius and Orphan stellar tidal streams with a new stream modeling framework, which uses a combination of particle spray models and N-body simulations in a Bayesian context. This work will measure the total masses of the MW and the LMC, and connect the orbits of the stream progenitors to their star formation and quenching. It will also provide a general software framework to the community for modeling other streams, and making detailed comparison to a range of observations with HST and other facilities. Galaxies and the IGM 0 Regular false false true SUPPORTED