Title: HST Proper Motions of Satellites and Streams

Abstract:
Dynamical studies of Satellites and Streams in the Galactic halo provide crucial information on 
the mass profile and accretion history of the Milky Way. However, the lack of knowledge on their 
transverse motions have been the main source of uncertainty in dynamical interpretation. To 
resolve this issue, accurate proper motion measurements are required for the objects of 
interest. We have recently developed a technique to measure absolute proper motions of 
resolved stellar systems using multi-epoch HST data by comparing shift of stars with respect to 
numerous background galaxies in the same fields. This technique has been successfully 
applied to galaxies and stellar streams in the Local Group. In this talk, I will present our past 
and ongoing HST projects for measuring absolute proper motions of Milky Way satellites (e.g., 
Draco, Sculptor, Leo I), stellar streams (e.g., Sagittarius, Orphan), and the metal-poor halo.