LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) is a Chinese national scientific research facility operated by National Astronomical Observatories, Chinese Academy of Sciences (NAOC). After two years of commissioning beginning in 2009, the telescope, instruments, software systems and operations are nearly ready to begin the main science survey. Through a spectral survey of millions of objects in much of the northern sky, LAMOST will enable research in a number of contemporary cutting edge topics in astrophysics, such as: discovery of the first generation stars in the Galaxy, pinning down the formation and evolution history of galaxies especially the Milky Way and its central massive black hole, looking for signatures of dark matter distribution and possible sub-structures in the Milky Way halo. To maximize the scientific potential of the facility, wide national participation and international collaboration has been emphasized. The survey has two major components: the LAMOST ExtraGAlactic Survey (LEGAS), and the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE). Until LAMOST reaches its full capability, the LEGUE portion of the survey will use the available observing time, starting in 2012. An overview of the LAMOST project and the survey that will be carried out in next five to six years is presented in this paper. The science plan for the whole LEGUE survey, instrumental specifications, site conditions, the descriptions of the current on-going pilot survey, including its footprints and target selection algorithm, will be presented as separate papers in this volume.

We derive new constraints on the mass of the Milky Way's dark matter halo, based on a set of halo stars from SDSS as kinematic tracers. Our sample comprises 2401 rigorously selected Blue Horizontal-Branch (BHB) halo stars at |z| ≥ 4 kpc, and with distances from the Galactic center up to ∼ 60 kpc, with photometry and spectra drawn from SDSS DR-6. With distances accurate to ∼ 10%,

We present and analyze the positions, distances, and radial velocities for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn from SDSS DR8. We search for position-velocity substructure in these data, a signature of the hierarchical assembly of the stellar halo. Using a cumulative "close pair distribution" (CPD) as a statistic in the 4-dimensional space of sky position, distance, and velocity, we quantify the presence of position-velocity substructure at high statistical significance among the BHB stars: pairs of BHB stars that

To constrain the Galactic gravitational potential near the Sun (∼1.5 kpc), we derive and model the spatial and velocity distribution for a sample of 9000 Kdwarfs with spectra from SDSS/SEGUE, which yield radial velocities and abundances ([Fe/H] & [α/Fe]). We first derive the spatial density distribution for three abundance-selected sub-populations of stars accounting for the survey's selection function. The vertical profile of these sub-populations are simple exponentials and their vertical dispersion profile is nearly isothermal. To model these data, we apply the 'vertical' Jeans Equation, which relates the observable tracer number density and vertical velocity dispersion to the gravitational potential or vertical force. We explore a number of functional forms for the vertical force law, and fit the dispersion and density profiles of all abundance selected sub-populations simultaneously in the same potential, and explore all parameter co-variances using MCMC. Our fits constrain a disk mass scale height 300 pc and the total surface mass density to be 67 ± 6 M pc −2 at |z| = 1.0 kpc of which the contribution from all stars is 42 ± 5 M pc −2 (presuming a contribution from cold gas of 13 M pc −2 ). We find significant constraints on the local dark matter density of 0.0065 ± 0.0023 M pc −3 (0.25 ± 0.09 GeV cm −3 ). Together with recent experiments this firms up the best estimate of 0.0075 ± 0.0021 M pc −3 (0.28 ± 0.08 GeV cm −3 ), consistent with global fits of approximately round dark matter halos to kinematic data in the outskirts of the Galaxy.