LSS-GAC – A LAMOST Spectroscopic Survey of the Galactic Anti-center

Abstract

AbstractAs a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) will survey a significant volume of the Galactic thin/thick disks and halo in a contiguous sky area of ~3,400 sq.deg., centered on the Galactic anti-center (|b| ≤ 30°, 150 ≤ l ≤ 210°), and obtain λλ3800–9000 low resolution (R ~1,800) spectra for a statistically complete sample of ≳ 3 M stars of all colors, uniformly and randomly selected from (r, g - r) and (r, r - i) Hess diagrams obtained from a CCD imaging photometric survey of ~5,400 sq.deg. with the Xuyi 1.04/1.20 m Schmidt Telescope, ranging from r = 14.0 to a limiting magnitude of r = 17.8 (18.5 for limited fields). The survey will deliver spectral classification, radial velocity (Vr) and stellar parameters (effective temperature (Teff), surface gravity (log g) and metallicity [Fe/H]) for millions of Galactic stars. Together with Gaia which will provide accurate distances and tangential velocities for a billion stars, the LSS-GAC will yield a unique data set to study the stellar populations, chemical composition, kinematics and structure of the disks and their interface with the halo, identify streams of debris of tidally disrupted dwarf galaxies and clusters, probe the gravitational potential and dark matter distribution, map the 3D distribution of interstellar dust extinction, search for rare objects (e.g. extremely metal-poor or hyper-velocity stars), and ultimately advance our understanding of the assemblage of the Milky Way and other galaxies and the origin of regularity and diversity of their properties.The survey was initiated in the fall of 2012 and expected to complete in the spring of 2017. Hitherto, about 0.4 M spectra of S/N(λ7450) ≥ 10 per pixel have been accumulated. In addition, bright nights have been used to target stars brighter than 14 mag and have so far generated over 0.4 M spectra, yielding an excellent sample of local stars to probe the solar neighborhood. LSP3, a set of pipelines tailored to the need of LSS-GAC, for spectral flux-calibration, and radial velocity and stellar parameter determinations, have been developed at Peking University, based on packages developed for the SDSS and those at the National Astronomical Observatories of Chinese Academy of Sciences. Comparisons of multi-epoch observations, with the SDSS results, as well as applying the pipelines to open and globular clusters show that LSP3 has achieved a precision of 5 km s−1, 110 K, 0.15 dex and 0.15 dex for Vr, Teff, log g and [Fe/H], respectively. The data are publicly available, subject to regulations of the LAMOST data policy, and begin to yield scientific results. The potential of LSS-GAC and power of existing data are illustrated with examples of selected problems.