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 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 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:
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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
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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.
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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
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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
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Note (1): Flag as follow:
0 = none;
1 = 552.8nm;
2 = 552.8 and 571.1nm.
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Byte-by-byte Description of file: table3.dat
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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
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History:
From electronic version of the journal
References:
Bergemann et al. 2012MNRAS.427...27B 2012MNRAS.427...27B Cat. J/MNRAS/427/27
Bergemann et al. Paper I. 2017ApJ...847...15B 2017ApJ...847...15B
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 28-May-2018