Presentation #210.05 in the session “The Milky Way, The Galactic Center 2”.
Previous studies of Milky Way stars have revealed that our Galaxy has a warped stellar disk, however, most of these studies have necessarily been confined to relatively nearby stars due to the challenge of deriving accurate stellar distances beyond the local volume. In contrast, to explore and characterize the warp over a much larger radial extent of the disk, we exploit the combination of the Gaia DR2 astrometric solution, stellar abundances from the APOGEE survey, and StarHorse distance estimates. The resulting database reveals a general decrease in stellar vertical velocities at Galactocentric radius R=13 kpc for stars with angular momentum Lz=2800 kpc km s-1, on which is superposed smaller ripples in vertical and radial velocity. We find that we can explain the decrease in vertical velocity using a simple analytical model of the Galactic warp having a starting radius of 8.87+0.08-0.09 kpc and a precession rate of 13.57+0.20-0.18 km s-1 kpc-1. That these parameters are similar across stellar age groups is evidence that the warp is an external, gravitationally induced phenomenon. We also find evidence suggesting that the Galactic warp is lopsided.