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.
