J/ApJ/847/16 NLTE spectroscopy. II. Galactic metal-poor stars (Bergemann+, 2017)
Non-local thermodynamic equilibrium stellar spectroscopy with 1D and <3D> models. II. Chemical properties of the Galactic metal-poor disk and the halo. Bergemann M., Collet R., Schonrich R., Andrae R., Kovalev M., Ruchti G., Hansen C.J., Magic Z. <Astrophys. J., 847, 16 (2017)> =2017ApJ...847...16B
ADC_Keywords: Stars, metal-deficient; Abundances; Equivalent widths Keywords: Galaxy: abundances; Galaxy: evolution; Galaxy: kinematics and dynamics; radiative transfer; stars: abundances; stars: late-type Abstract: From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (local thermodynamic equilibrium (LTE), 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature and, in particular, for LTE versus non-LTE (NLTE), on metallicity of the stars. Here we analyze the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged <3D> models. We show that compared to the <3D> NLTE benchmark, the other three methods display increasing biases toward lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best <3D> NLTE model, the halo and disk stars show a clearer behavior in the [Mg/Fe]-[Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disk stars and this population extends down to at least [Fe/H]~-1.6dex, further than previously proven. The thick disk stars display a constant [Mg/Fe]∼0.3dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disk formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo. Description: The stars were selected from the RAVE Survey (Steinmetz+ 2006AJ....132.1645S) to study a large sample of metal-poor stars with thick disk-like kinematics and observed at high-resolution (R>30000) at several facilities, including FEROS on the MPG 2.2m telescope, the MIKE spectrograph on the Magellan-Clay telescope, the ARC spectrograph on the Apache Point 3.5m telescope, and the UCLES spectrograph on the Anglo-Australian telescope. All spectra except those taken with UCLES cover the full optical range from ∼3500 to ∼9500Å. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 112 319 *Stellar parameters and derived Mg abundances for the stellar sample table3.dat 35 319 Measurements of the equivalent widths of the two MgI diagnostic
Note on table1.dat: We assumed two different sets of input stellar parameters: 1D LTE and non-local thermodynamic equilibrium (NLTE)-opt, as described in Ruchti+ (2013, J/MNRAS/429/126). 1D LTE values were determined by the classical method of LTE excitation-ionization balance of Fe lines. Our second input data set was NLTE-opt, for which accurate estimates for the effective temperature (Teff), surface gravity (logg), and metallicity of the stars were determined as described in section 2.
See also: III/257 : RAVE second data release (Zwitter+, 2008) III/279 : RAVE 5th data release (Kunder+, 2017) I/337 : Gaia DR1 (Gaia Collaboration, 2016) I/345 : Gaia DR2 (Gaia Collaboration, 2018) J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004) J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010) J/A+A/530/A138 : Geneva-Copenhagen survey re-analysis (Casagrande+, 2011) J/A+A/530/A54 : Abundances of 650 bulge red giants (Gonzalez+, 2011) J/ApJ/737/9 : RAVE data of stars in the thick disk (Ruchti+, 2011) J/A+A/546/A90 : NLTE analysis of Sr lines (Bergemann+, 2012) J/A+A/557/A26 : STAGGER-grid of 3D stellar models. I. (Magic+, 2013) J/MNRAS/429/126 : Atmospheric parameters from Fe lines (Ruchti+, 2013) J/A+A/562/A71 : Abundances of solar neighbourhood dwarfs (Bensby+, 2014) J/A+A/572/A10 : (BV) photometry in Carina dSph (de Boer+, 2014) J/A+A/572/A88 : Measured EWs for Fornax RGB stars (Lemasle+, 2014) J/AJ/148/81 : APASS BVgri photometry of RAVE stars. I. Data (Munari+, 2014) J/A+A/584/A46 : GIRAFFE Inner Bulge Survey (GIBS). II. (Gonzalez+, 2015) J/AJ/151/144 : Weights for 15 APOGEE chemical elements (Garcia+, 2016) J/ApJ/819/2 : APOGEE kinematics. I. Galactic bulge overview (Ness+, 2016) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 21 A21 --- Name Simbad data-base identifier 23- 26 I4 K Teff1 [4004/6531] LTE-Fe effective temperature 28- 31 F4.2 [cm/s2] log(g)1 [0.5/4.4] LTE-Fe surface gravity 33- 37 F5.2 [Sun] [Fe/H]1 [-3.2/-0.3] LTE-Fe metallicity 39- 42 F4.2 km/s V1 [0.5/3] LTE-Fe microturbulence 44- 47 I4 K Teff2 [4043/6519] NLTE-Opt effective temperature 49- 52 F4.2 [cm/s2] log(g)2 [0.5/4.6] NLTE-Opt surface gravity 54- 58 F5.2 [Sun] [Fe/H]2 [-2.8/-0.4] NLTE-Opt metallicity 60- 63 F4.2 km/s V2 [0.5/3.3] NLTE-Opt microturbulence 65- 69 F5.2 [Sun] [Mg]1 [-0.03/0.7]? Log Mg/Fe abundance ratio: 1D LTE 71- 74 F4.2 [Sun] e_[Mg]1 [0.1/0.3]? Uncertainty in [Mg]1 76- 80 F5.2 [Sun] [Mg]2 [-0.02/0.7]? Log Mg/Fe abundance ratio: NLTE-opt & LTE Mg 82- 85 F4.2 [Sun] e_[Mg]2 [0.1/0.3]? Uncertainty in [Mg]2 87- 91 F5.2 [Sun] [Mg]3 [-0.04/0.6]? Log Mg/Fe abundance ratio: NLTE-opt & NLTE Mg 93- 96 F4.2 [Sun] e_[Mg]3 [0.1/0.3]? Uncertainty in [Mg]3 98-101 F4.2 [Sun] [Mg]4 [0.02/0.6]? Log Mg/Fe abundance ratio: NLTE-opt & <3D> NLTE Mg 103-106 F4.2 [Sun] e_[Mg]4 [0.1/0.3]? Uncertainty in [Mg]4 108 I1 --- Flag [0/2]? Number of measured Mg I lines (1) 110-112 F3.1 --- Pop [1/3] Galactic population assignment
Note (1): Flag as follow: 0 = none; 1 = 552.8nm; 2 = 552.8 and 571.1nm.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 21 A21 --- Name Simbad data-base identifier 23- 28 F6.2 10-13m EW1 [41.9/267.1]? Equivalent width of the 552.8nm MgI line 30- 35 F6.2 10-13m EW2 [2.3/143.5]? Equivalent width of the 571.1nm MgI line
History: From electronic version of the journal References: Bergemann et al. 2012MNRAS.427...27B Cat. J/MNRAS/427/27 Bergemann et al. Paper I. 2017ApJ...847...15B
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 28-May-2018
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