J/MNRAS/429/126 Atmospheric parameters from Fe lines (Ruchti+, 2013)
Unveiling systematic biases in the 1D LTE excitation-ionization balance of Fe
for FGK stars: a novel approach to determination of stellar parameters.
Ruchti G.R., Bergemann M., Serenelli A., Casagrande L., Lind K.
<Mon. Not. R. Astron. Soc., 429, 126-134 (2013)>
=2013MNRAS.429..126R 2013MNRAS.429..126R
ADC_Keywords: Stars, late-type ; Effective temperatures
Keywords: stars: abundances - stars: late-type - stars: Population II -
radiative transfer - methods: data analysis -
techniques: spectroscopic
Abstract:
We present a comprehensive analysis of different techniques available
for the spectroscopic analysis of FGK stars and provide a recommended
methodology which efficiently estimates accurate stellar atmospheric
parameters for large samples of stars. Our analysis includes a
simultaneous equivalent width analysis of FeI and FeII spectral lines,
and for the first time, utilizes on-the-fly non-local thermodynamic
equilibrium (NLTE) corrections of individual FeI lines. We further
investigate several temperature scales, finding that estimates from
Balmer line measurements provide the most accurate effective
temperatures at all metallicities. We apply our analysis to a large
sample of both dwarf and giant stars selected from the Radial Velocity
Experiment (RAVE) survey. We then show that the difference between
parameters determined by our method and that by the standard 1D LTE
excitation-ionization balance of Fe reveals substantial systematic
biases: up to 400K in effective temperature, 1.0dex in surface
gravity and 0.4dex in metallicity for stars with [Fe/H]~-2.5. This
has large implications for the study of the stellar populations in the
Milky Way.
Description:
Full details of the observations and data reduction of the spectra can
be found in Ruchti et al. (2011, Cat. J/ApJ/737/9). Briefly, all
spectrographs delivered a resolving power greater than 30000 and
covered the full optical wavelength range. Further, nearly all
spectra had signal-to-noise ratios greater than 100:1 per pixel.
The equivalent widths (EWs) of both FeI and FeII lines, taken from
the line lists of Fulbright (2000, Cat. J/AJ/120/1841) and Johnson
(2002ApJS..139..219J 2002ApJS..139..219J), were measured using the ARES code (Sousa et al.
2007, Cat. J/A+A/469/783). However, during measurement quality checks,
we found that the continuum was poorly estimated for some lines.
We therefore determined EWs for these affected lines using hand
measurements.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 92 319 Atmospheric stellar parameter data
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See also:
J/A+A/469/783 : Code for automatic determination of EW (ARES) (Sousa+, 2007)
J/A+A/512/A54 : Teff and Fbol from Infrared Flux Method (Casagrande+, 2010)
J/AJ/120/1841 : Abundances & kinematics of halo and disk stars (Fulbright 2000)
J/ApJ/737/9 : Thick disk stars RAVE spectroscopic data (Ruchti+, 2011)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Name Star name, as in Ruchti et al. 2011,
Cat. J/ApJ/737/9
18- 21 I4 K Teff1 LTE-Fe effective temperature (1)
23- 24 I2 K e_Teff1 rms uncertainty on TeffL (1)
26- 29 F4.2 [cm/s2] logg1 LTE-Fe surface gravity (error ±0.1) (1)
31- 35 F5.2 [Sun] [Fe/H]1 LTE-Fe metallicity (error ±0.1) (1)
37- 39 F3.1 km/s v1 LTE-Fe microturbulence velocity (1)
41- 45 F5.3 mag E(B-V) ?=- Redenning
47- 50 I4 K TIRFM ?=- IRFM temperature (2)
52- 54 I3 K e_TIRFM ?=- rms uncertainty on TIRFM (2)
56- 59 I4 K TR11 Temperature from Ruchti et al. 2011,
Cat. J/ApJ/737/9
61- 64 I4 K TBal ?=- Temperature estimated from Balmer lines
66- 68 I3 K e_TBal ?=- rms uncertainty on TBal
70- 73 I4 K Teff2 NLTE-Opt effective temperature (1)
75- 77 I3 K e_Teff2 rms uncertainty on TeffN (1)
79- 82 F4.2 [cm/s2] logg2 NLTE-Opt surface gravity (error ±0.1) (1)
84- 88 F5.2 [Sun] [Fe/H]2 NLTE-Opt metallicity (error ±0.1) (1)
90- 92 F3.1 km/s v2 NLTE-Opt microturbulence velocity (1)
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Note (1): Methods used for the computation of the atmospheric parameters:
LTE-Fe = from the ionisation and excitation equilibrium of the Fe ions
in Local Thermodynamic Equilibrium
NLTE-Opt = Non-Local Thermodynamic Equilibrium, Optimal estimate of
effective temperature, then the surface gravity, metallicity,
[Fe/H] and microturbulence.
Note (2): IRFM = infrared flux method, presented in Casagrande et al. (2010,
ser Cat. J/A+A/512/A54)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 14-Mar-2014