The First Data Release (DR1) of the LAMOST general survey (1505.01570v1)

Abstract: The Large sky Area Multi-Object Spectroscopic Telescope (LAMOST) General Survey is a spectroscopic survey that will eventually cover approximately half of the celestial sphere and collect 10 million spectra of stars, galaxies and QSOs. Objects both in the pilot survey and the first year general survey are included in the LAMOST First Data Release (DR1). The pilot survey started in October 2011 and ended in June 2012, and the data have been released to the public as the LAMOST Pilot Data Release in August 2012. The general survey started in September 2012, and completed its first year of operation in June 2013. The LAMOST DR1 includes a total of 1202 plates containing 2,955,336 spectra, of which 1,790,879 spectra have observed signal-to-noise S/N >10. All data with S/N>2 are formally released as LAMOST DR1 under the LAMOST data policy. This data release contains a total of 2,204,696 spectra, of which 1,944,329 are stellar spectra, 12,082 are galaxy spectra and 5,017 are quasars. The DR1 includes not only spectra, but also three stellar catalogues with measured parameters: AFGK-type stars with high quality spectra (1,061,918 entries), A-type stars (100,073 entries), and M stars (121,522 entries). This paper introduces the survey design, the observational and instrumental limitations, data reduction and analysis, and some caveats. Description of the FITS structure of spectral files and parameter catalogues is also provided.

Overview of the LAMOST First Data Release (DR1) General Survey

The paper discusses the first data release (DR1) of the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope) general survey, providing a comprehensive overview of its design, execution, data reduction, analysis, and limitations. Located at the Xinglong Observatory in China, LAMOST is distinguished by its large field of view and extensive fiber multiplexing capabilities, allowing for efficient acquisition of stellar spectra. This release includes data procured from both the pilot and the first year of the general survey, comprising a total of 2,204,860 spectra covering diverse astronomical objects such as stars, galaxies, and quasars.

Survey Design and Objectives

LAMOST's survey is divided into two main components: LEGUE (LAMOST Experiment for Galactic Understanding and Exploration) and LEGAS (LAMOST ExtraGAlactic Survey). LEGUE primarily focuses on the Galactic survey, targeting areas like the Galactic anti-center and disk, while LEGAS is dedicated to extragalactic sources including galaxies and quasars. The survey aims to rigorously sample diverse stellar populations within the Milky Way, offering insights into Galactic structure and evolution.

Data Reduction and Analysis

The paper details robust data processing methodologies applied to the acquired spectra. The LAMOST 2D pipeline handles raw CCD data, performing functions such as dark subtraction, flat field correction, sky subtraction, and wavelength calibration. The 1D pipeline classifies spectra into stars, galaxies, and quasars, providing measurements of radial velocity or redshift. For stars, the LAMOST Stellar Parameter Pipeline (LASP) calculates key stellar atmospheric parameters like effective temperature (Teff), surface gravity (logg), and metallicity ([Fe/H]) with methods such as Correlation Function Interpolation (CFI) and ULySS. These methods assure the accurate derivation of stellar parameters despite challenges like relative flux calibration and instrumental uncertainties.

Key Results and Observations

The DR1 release comprises 1,944,329 stellar spectra, 12,082 galaxy spectra, and 5,017 quasar spectra. The DR1 data quality is assessed using parameters such as signal-to-noise ratios (SNR), with successful observations characterized predominantly by SNR >10 in g- or i-band. The spectral resolution achieved is approximately R > 1500, exceeding initial theoretical expectations. The paper also notes systematic errors affecting the data, including radial velocity inaccuracies due to incorrect heliocentric corrections and issues related to exposure combination.

Implications and Future Perspectives

This data release represents a significant advancement in large-scale spectroscopic surveys, enabling extensive scientific exploration of both Galactic and extragalactic phenomena. The sophisticated data reduction techniques and comprehensive cataloging efforts offer a rich repository of information that can catalyze further astrophysical research. However, various instrumental and observational limitations—such as fiber positioning accuracy and dome seeing—are identified as areas for future improvement. The ongoing refinement of spectral analysis methodologies and instrumentation is likely to enhance the precision of subsequent data releases.

Conclusion

The LAMOST DR1 provides a substantial contribution to the field of astrophysics, laying groundwork for exploring the Galactic structure and beyond. It sets a precedent for future spectroscopic surveys, emphasizing the importance of addressing technical limitations and improving observational strategies. As LAMOST continues its operations, the forthcoming data releases are anticipated to drive deeper insights into the dynamics and composition of celestial entities.