Fishing in Tidal Streams: New Radial Velocity and Proper Motion Constraints on the Orbit of the Anticenter Stream

We have obtained radial velocity measurements for stars in two, widely-separated fields in the Anticenter Stream. Combined with SDSS/USNO-B proper motions, the new measurements allow us to establish that the stream is on a nearly circular, somewhat inclined, prograde orbit around the Galaxy. While the orbital eccentricity is similar to that previously determined for the Monoceros stream, the sizes, inclinations, and positions of the orbits for the two systems differ significantly. Integrating our best fitting Anticenter Stream orbit forward, we find that it is closely aligned along and lies almost on top of a stream-like feature previously designated the "Eastern Banded Structure". The position of this feature coincides with the apogalacticon of the orbit. We tentatively conclude that this feature is the next wrap of the Anticenter Stream.