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

TL;DR

This study maps the U-V velocity distribution of about 15,000 nearby dwarf stars from the LAMOST survey, revealing known and new substructures likely influenced by the Galactic bar, advancing understanding of local stellar dynamics.

Contribution

It introduces an empirical multi-Gaussian model of the local velocity distribution using an extreme deconvolution algorithm, unveiling new substructures and their possible origins.

Findings

Identification of new substructures in the U-V velocity plane.

Detection of a ripple-like structure possibly linked to the Galactic bar.

Observation that certain over-densities are aligned, suggesting common origins.

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 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.