The Velocity of the Local Standard of Rest Using Sagittarius Tidal Debris

Dana Casetti

To date, the Sagittarius dwarf galaxy (Sgr) offers the best opportunity to study the Milky Way's gravitational potential as inferred from tidal streams. Sgr's polar orbit, with the orbital plane nearly coincident with the X-Z Galactic plane makes the Sgr tidal stream an ideal measuring tool of the rotation of the Local Standard of Rest. Specifically, transverse velocities of stars in Sgr's trailing tail are mainly due to the reflex Solar motion. Our deep, precise proper-motion survey in Kapteyn Selected Areas (SA) offers this opportunity. Preliminary results shown in the figure include model predictions (proper motions as a function of angular distance from Sgr's core) for Sgr debris for two LSR velocities, and our measurements in two SA fields. Our collaborators at the Univ. of Virginia provide photometry and radial velocities in order to better select Sgr members.