Browsing by Subject "apogee"
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Item Calibrations Of Atmospheric Parameters Obtained From The First Year Of Sdss-III APOGEE Observations(2013-11) Meszaros, S.; Holtzman, J.; Perez, A. E. Garcia; Prieto, C. Allende; Schiavon, R. P.; Basu, S.; Bizyaev, D.; Chaplin, W. J.; Chojnowski, S. D.; Cunha, K.; Elsworth, Y.; Epstein, C.; Frinchaboy, P. M.; Garcia, R. A.; Hearty, F. R.; Hekker, S.; Johnson, J. A.; Kallinger, T.; Koesterke, L.; Majewski, S. R.; Martell, S. L.; Nidever, D.; Pinsonneault, M. H.; O'Connell, J.; Shetrone, M.; Smith, V. V.; Wilson, J. C.; Zasowski, G.; Koesterke, L.The Sloan Digital Sky Survey III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a three-year survey that is collecting 105 high-resolution spectra in the near-IR across multiple Galactic populations. To derive stellar parameters and chemical compositions from this massive data set, the APOGEE Stellar Parameters and Chemical Abundances Pipeline (ASPCAP) has been developed. Here, we describe empirical calibrations of stellar parameters presented in the first SDSS-III APOGEE data release (DR10). These calibrations were enabled by observations of 559 stars in 20 globular and open clusters. The cluster observations were supplemented by observations of stars in NASA's Kepler field that have well determined surface gravities from asteroseismic analysis. We discuss the accuracy and precision of the derived stellar parameters, considering especially effective temperature, surface gravity, and metallicity; we also briefly discuss the derived results for the abundances of the a-elements, carbon, and nitrogen. Overall, we find that ASPCAP achieves reasonably accurate results for temperature and metallicity, but suffers from systematic errors in surface gravity. We derive calibration relations that bring the raw ASPCAP results into better agreement with independently determined stellar parameters. The internal scatter of ASPCAP parameters within clusters suggests that metallicities are measured with a precision better than 0.1 dex, effective temperatures better than 150 K, and surface gravities better than 0.2 dex. The understanding provided by the clusters and Kepler giants on the current accuracy and precision will be invaluable for future improvements of the pipeline.Item New H-Band Stellar Spectral Libraries For The SDSS-III/APOGEE Survey(2015-06) Zamora, O.; Garcia-Hernandez, D. A.; Prieto, C. A.; Carrera, R.; Koesterke, L.; Edvardsson, B.; Castelli, F.; Plez, B.; Bizyaev, D.; Cunha, K.; Perez, A. E. G.; Gustafsson, B.; Holtzman, J. A.; Lawler, J. E.; Majewski, S. R.; Manchado, A.; Meszaros, S.; Shane, N.; Shetrone, M.; Smith, V. V.; Zasowski, G.; Koesterke, L.The Sloan Digital Sky Survey-III (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) has obtained high-resolution (R similar to 22,500), high signal-to-noise ratio (>100) spectra in the H-band (similar to 1.5-1.7 mu m) for about 146,000 stars in the Milky Way galaxy. We have computed spectral libraries with effective temperature (T-eff) 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-eff = 3500-8000 K) and MARCS/Turbospectrum (T-eff = 3500-5500 K) grids cover a wide range of metallicity (-2.5 <= [M/H] <= + 0.5 dex), surface gravity (0 <= log g <= 5 dex), microturbulence (0.5 <= xi <= 8 km s(-1)), carbon (-1 <= [C/M] <= + 1 dex), nitrogen (-1 <= [N/M] <= + 1 dex), and alpha-element (-1 <= [alpha/M] <= + 1 dex) variations, having thus seven dimensions. We compare the ATLAS9/ASS.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.