The velocity distribution in the solar neighbourhood from the LAMOST   pilot survey
  We use about 15,000 F/G nearby dwarf stars selected from the LAMOST pilot survey to map the U-V velocity distribution in the solar neighbourhood. An extreme deconvolution algorithm is applied to reconstruct an empirical multi-Gaussian model. In addition to the well known substructures, e.g., Sirius, Coma Berenices, Hyades-Pleiades over-densities, several new substructures are unveiled. A ripple-like structure from (U, V) = (-120, -5) to (103, -32)km/s is clearly seen in the U-V distribution. This structure seems associated with resonance induced by the Galactic bar, since it is extended in U while having a small dispersion in V at the same time. A ridge structure between (U, V) = (-60, 40) and (-15, 15) km/s is also found. Although similar substructures have been seen in the Hipparcos data, their origin is still unclear. Another compact over-density is seen at (U, V) = (-102, -24). With this large data sample, we find that the substructure located at V~70 km/s and the Arcturus group are essentially parallel in V, which may indicate that they originate from an unrelaxed disk component perturbed by the rotating bar. 
Qiran Xia, Chao Liu, Yan Xu, Shude Mao, Shuang Gao, Yonghui Hou, Ge   Jin, Yong Zhang
astro-ph.GA