2018ApJ...864..129H

Using a sample of about 123,000 stars with accurate 3D velocity measurements from the LAMOST-TGAS data, we confirm the kinematic signature of the Galactic warp recently found by Schonrich & Dehnen. The data reveal a clear trend of increasing mean vertical velocity  as a function of absolute vertical angular momentum L_z and azimuthal velocity V_ph for guiding center radius R_g between 6.0 and 10.5 kpc. The trend is consistent with a large-scale Galactic warp. Similar to Schonrich & Dehnen, we also find a wave-like pattern of  versus L_z with an amplitude of ∼0.9 km s^–1 on a scale of ∼2.0 kpc, which could arise from bending waves or a winding warp. Finally, we confirm a prominent, localized peak in  near L_z ∼ 2150 kpc km s^–1 (corresponding to R_g ∼ 9 kpc and V_ph ∼ 255 km s^–1). The additional line-of-sight velocity information from LAMOST reveals that stars in this feature have a large, inward radial velocity of V_R ∼ -13.33 ± 0.59 km s^–1 and a small radial velocity dispersion of σ_R ∼ 25.27 ± 0.89 km s^–1, suggesting that a stellar stream gives rise to this feature.