New H-band Stellar Spectral Libraries for the SDSS-III/APOGEE Survey

Abstract

The Sloan Digital Sky Survey-III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) has obtained high-resolution (R ~ 22,500), high signal-to-noise ratio (\gt 100) spectra in the H-band (~1.5--1.7 mum) for about 146,000 stars in the Milky Way galaxy. We have computed spectral libraries with effective temperature ({{T}<SUB>eff</SUB>}) ranging from 3500 to 8000 K for the automated chemical analysis of the survey data. The libraries, used to derive stellar parameters and abundances from the APOGEE spectra in the SDSS-III data release 12 (DR12), are based on ATLAS9 model atmospheres and the ASS&epsilon;T spectral synthesis code. We present a second set of libraries based on MARCS model atmospheres and the spectral synthesis code Turbospectrum. The ATLAS9/ASS&epsilon;T ({{T}<SUB>eff</SUB>} = 3500--8000 K) and MARCS/Turbospectrum ({{T}<SUB>eff</SUB>} = 3500--5500 K) grids cover a wide range of metallicity (-2.5 <=slant [M/H] <=slant +0.5 dex), surface gravity (0 <= log g <=slant 5 dex), microturbulence (0.5 <=slant xi <=slant 8 km s<SUP>-1</SUP>), carbon (-1 <=slant [C/M] <=slant +1 dex), nitrogen (-1 <=slant [N/M] <=slant +1 dex), and alpha-element (-1 <=slant [alpha/M] <=slant +1 dex) variations, having thus seven dimensions. We compare the ATLAS9/ASS&epsilon;T and MARCS/Turbospectrum libraries and apply both of them to the analysis of the observed H-band spectra of the Sun and the K2 giant Arcturus, as well as to a selected sample of well-known giant stars observed at very high resolution. The new APOGEE libraries are publicly available and can be employed for chemical studies in the H-band using other high-resolution spectrographs.