The velocity distribution in the solar neighbourhood from the LAMOST pilot survey

Abstract

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 wellknown substructures, e.g. Sirius, Coma Berenices, Hyades-Pleiades overdensities, several new substructures are unveiled. A ripple-like structure from (U, V) = (-120, -5) to (103, -32) km s-1 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-1 is also found. Although similar substructures have been seen in the Hipparcos data, their origin is still unclear. Another compact overdensity is seen at (U, V) = (-102, -24). With this large data sample, we find that the substructure located at V~-70 km s-1 and the Arcturus group are essentially parallel in V, which may indicate that they originate from an unrelaxed disc component perturbed by the rotating bar.