The Sloan Extension for Galactic Understanding and Exploration 2 (SEGUE-2) obtained 128,288 low-resolution spectra (R ∼1800) of 118,958 unique stars in the first year of the Sloan Digital Sky Survey III (2008-2009). SEGUE-2 targeted prioritized distant halo tracers (blue horizontal-branch stars, K giants, and M giants) and metal-poor or kinematically hot populations. The main goal of SEGUE-2 was to target stars in the distant halo and measure their kinematics and chemical abundances to learn about the formation and evolution of the Milky Way. We present the SEGUE-2 field placement and target selection strategies. We discuss the success rate of the targeting based on the SEGUE-2 spectra and other spectroscopic and astrometric surveys. We describe the final SEGUE-2/SDSS-III improvements to the stellar parameter determinations based on the SEGUE Stellar Parameter Pipeline. We report a (g - i) color-effective temperature relation calibrated to the IRFM. We evaluate the accuracy and uncertainties associated with these stellar parameters by comparing with fundamental parameters, a sample of high-resolution spectra of SEGUE stars analyzed homogeneously, stars in well-studied clusters, and stars observed in common by the APOGEE survey. The final SEGUE spectra, calibration data, and derived parameters described here were released in SDSS-III Data Release 9 and continue to be included in all subsequent SDSS Data Releases. Because of its faint limiting magnitude and emphasis on the distant halo, the public SEGUE-2 data remain an important resource for the spectroscopy of stars in the Milky Way.
Bibliographical noteFunding Information:
C.M.R. acknowledges support from the David and Lucille Packard Foundation. H.L.M. thanks the National Science Foundation for support for this work under grant AST-1009886. H.L.M., C.M.R., and P.H. thank the NSF for support with grant AST-121989. P.H. thanks the NSF for their support under grant AST-1211144. The work was also supported in part by the National Science Foundation under grant No. PHYS-1066293 and the hospitality of the Aspen Center for Physics. L.C. is the recipient of ARC Future Fellowship FT160100402. D.A. acknowledges support from the NRF of Korea (NRF-2021R1A2C1004117). T.C.B. and Y.S.L. acknowledge partial support from grant PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation. Y.S.L. acknowledges support from the National Research Foundation (NRF) of Korea grant funded by the Ministry of Science and ICT (NRF-2018R1A2B6003961 and NRF-2021R1A2C1008679). We thank the Hobby–Eberly Telescope TAC for an important early allocation of time for the calibration data.
Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the US Department of Energy Office of Science. The SDSS-III website is http://www.sdss3.org/ .
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