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تسجيل مستخدم جديدThe SDSS-III APOGEE Spectral Line List for H-band Spectroscopy
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We present the $H$-band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the APOGEE line list, which is one of the critical inputs for the APOGEE Stellar Parameters and Chemical Abundances Pipeline, and present three differe
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The Sloan Digital Sky Survey--III (SDSS--III) Apache Point Observatory Galactic Evolution Experiment (APOGEE) has obtained high resolution (R $sim$ 22,500), high signal-to-noise ratio ($>$ 100) spectra in the H$-$band ($sim$1.5$-$1.7 $mu$m) for about
146,000 stars in the Milky Way galaxy. We have computed spectral libraries with effective temperature ($Trm{_{eff}}$) ranging from 3500 to 8000 K for the automated chemical analy-sis 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 ($Trm{_{eff}}$ = 3500$-$8000 K) and MARCS/Turbospectrum ($Trm{_{eff}}$ = 3500$-$5500 K) grids cover a wide range of metallicity ($-$2.5 $leq$ [M/H] $leq$ $+$0.5 dex), surface gravity (0 $leq$ log $g$ $leq$ 5 dex), microturbulence (0.5 $leq$ $xi$ $leq$ 8 km~s$^{-1}$), carbon ($-$1 $leq$ [C/M] $leq$ $+$1 dex), nitrogen ($-$1 $leq$ [N/M] $leq$ $+$1 dex), and $alpha$-element ($-$1 $leq$ [$alpha$/M] $leq$ $+$1 dex) variations, having thus seven dimensions. We compare the ATLAS9/ASS$epsilon$T and MARCS/Turbospectrum libraries and apply both of them to the analysis of the observed H$-$band spectra of the Sun and the K2 giant Arcturus, as well as to a selected sample of well-known giant stars observed at very high-resolution. The new APOGEE libraries are publicly available and can be employed for chemical studies in the H$-$band using other high-resolution spectrographs.
Integrated light spectroscopy from galaxies can be used to study the stellar populations that cannot be resolved into individual stars. This analysis relies on stellar population synthesis (SPS) techniques to study the formation history and structure
of galaxies. However, the spectral templates available for SPS are limited, especially in the near-infrared. We present A-LIST (APOGEE Library of Infrared SSP Templates), a new set of high-resolution, near-IR SSP spectral templates spanning a wide range of ages (2-12 Gyr), metallicities ($rm -2.2 < [M/H] < +0.4$) and $alpha$ abundances ($rm -0.2 < [alpha/M] < +0.4$). This set of SSP templates is the highest resolution ($Rsim22500$) available in the near infrared, and the first such based on an empirical stellar library. Our models are generated using spectra of $sim$300,000 stars spread across the Milky Way, with a wide range of metallicities and abundances, from the APOGEE survey. We show that our model spectra provide accurate fits to M31 globular cluster spectra taken with APOGEE, with best-fit metallicities agreeing with those of previous estimates to within $sim$0.1 dex. We also compare these model spectra to lower-resolution E-MILES models and demonstrate that we recover the ages of these models to within $sim$1.5 Gyr. This library is available in https://github.com/aishashok/ALIST-library.
The updated H-band spectral line list (from lambda 15,000 - 17,000AA) adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) for the SDSS IV Data Release 16 (DR16) is presented here. The APOGEE line list is a combination of at
omic and molecular lines with data from laboratory, theoretical, and astrophysical sources. Oscillator strengths and damping constants are adjusted using high signal-to-noise, high-resolution spectra of the Sun and alpha Boo (Arcturus) as standard stars. Updates to the DR16 line list, when compared to the previous DR14 version, are the inclusion of molecular H_2O and FeH lines, as well as a much larger (by a factor of ~4) atomic line list, which includes significantly more transitions with hyperfine splitting. More recent references and line lists for the crucial molecules CO and OH were used, as well as for C_2 and SiH. In contrast to DR14, DR16 contains measurable lines from the heavy neutron-capture elements cerium (as Ce II), neodymium (as Nd II), and ytterbium (as Yb II), as well as one line from rubidium (as Rb I), that may be detectable in a small fraction of APOGEE red giants.
APOGEE has amassed the largest ever collection of multi-epoch, high-resolution (R~22,500), H-band spectra for B-type emission line (Be) stars. The 128/238 APOGEE Be stars for which emission had never previously been reported serve to increase the tot
al number of known Be stars by ~6%. We focus on identification of the H-band lines and analysis of the emission peak velocity separations (v_p) and emission peak intensity ratios (V/R) of the usually double-peaked H I and non-hydrogen emission lines. H I Br11 emission is found to preferentially form in the circumstellar disks at an average distance of ~2.2 stellar radii. Increasing v_p toward the weaker Br12--Br20 lines suggests these lines are formed interior to Br11. By contrast, the observed IR Fe II emission lines present evidence of having significantly larger formation radii; distinctive phase lags between IR Fe II and H I Brackett emission lines further supports that these species arise from different radii in Be disks. Several emission lines have been identified for the first time including ~16895, a prominent feature in the spectra for almost a fifth of the sample and, as inferred from relatively large v_p compared to the Br11-Br20, a tracer of the inner regions of Be disks. Unlike the typical metallic lines observed for Be stars in the optical, the H-band metallic lines, such as Fe II 16878, never exhibit any evidence of shell absorption, even when the H I lines are clearly shell-dominated. The first known example of a quasi-triple-peaked Br11 line profile is reported for HD 253659, one of several stars exhibiting intra- and/or extra-species V/R and radial velocity variation within individual spectra. Br11 profiles are presented for all discussed stars, as are full APOGEE spectra for a portion of the sample.
The SDSS-III/APOGEE survey operated from 2011-2014 using the APOGEE spectrograph, which collects high-resolution (R~22,500), near-IR (1.51-1.70 microns) spectra with a multiplexing (300 fiber-fed objects) capability. We describe the survey data produ
cts that are publicly available, which include catalogs with radial velocity, stellar parameters, and 15 elemental abundances for over 150,000 stars, as well as the more than 500,000 spectra from which these quantities are derived. Calibration relations for the stellar parameters (Teff, log g, [M/H], [alpha/M]) and abundances (C, N, O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Mn, Fe, Ni) are presented and discussed. The internal scatter of the abundances within clusters indicates that abundance precision is generally between 0.05 and 0.09 dex across a broad temperature range; within more limited ranges and at high S/N, it is smaller for some elemental abundances. We assess the accuracy of the abundances using comparison of mean cluster metallicities with literature values, APOGEE observations of the solar spectrum and of Arcturus, comparison of individual star abundances with other measurements, and consideration of the locus of derived parameters and abundances of the entire sample, and find that it is challenging to determine the absolute abundance scale; external accuracy may be good to 0.1-0.2 dex. Uncertainties may be larger at cooler temperatures (Teff<4000K). Access to the public data release and data products is described, and some guidance for using the data products is provided.
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