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3D and NLTE analysis for large stellar surveys
Karin LindUppsala University, Sweden
Martin Asplund, Paul Barklem, Andrey Belyaev, Maria Bergemann, Remo Collet, Zazralt Magic, Anna Marino, Jorge Meléndez, Yeisson Osorio
Outline
- Introduction- 1D LTE/NLTE
- Worst-case scenarios- Recent progress- Calibration techniques- Practical implementation- Applications
- 3D LTE/NLTE- Worst-case scenarios- Observational tests- Mg : 1D/<3D>/LTE/NLTE- Ca : 1D/<3D>/3D/LTE/NLTE - Applications
Motivation
Galactic archaeology by chemical tagging of FGK stars
- Statistics : Soon > 106 stars
- Precision (S/N, wavelength range) : σ[X/H] < 0.1dex, σTeff<150K, σlog(g)<0.3dex
- Accuracy (assumptions: 1D, LTE, atomic data) : σ [X/H]< 0.5 dex, σTeff<400K, σlog(g)< 1 dex
Methods
Model atmosphere Detailed rad. Transfer1D/<3D>/3D LTE 1D/3D LTE/NLTE
R. Collet
NLTE line formation
(1D)
Is it really necessary?
Is it safe?
N-
Worst-case scenario I
NaD lines in metal-poor horisontal branch stars Lind et al. 2011, Marino et al. 2011
B-I
Worst-case scenario II
OI 777nm triplet at very low metallicities
Fabbian et al. 2009
LTE trend
Input data for NLTE analysis
Energy levels + oscillator strengths + photo-ionization cross sectionsRed boxes : have sufficient(?) data
Blue boxes : missing e.g. QM photo-ionisation, but NLTE still attempted
Input data for NLTE analysis
Blue boxes : QM hydrogen collisions exist or will exist
Input data for NLTE analysis
Solar neighborhood MDF Halo MDF [X/Fe] vs [Fe/H]
Most important free parameter in NLTEmodelling of Fe is FeI+HI collisional cross-section
Black – LTE Blue – NLTE with no hydrogen collisions
Calibration techniques: ionisation balance
Korn et al. 2003
FeI/FeII ionisation equilibrium calibrated using Hipparcos gravities
S(H)=3
Calibration techniques: excitation balance
Bergemann & Gehren 2008
“Thus, NLTE can solve the discrepancy between the abundances derived from the MnI resonance triplet at 403 nm and excited lines, which is found in analyses of metal-poor subdwarfs and subgiants”
S(H)=0.05
Calibration techniques: CLV
Allende Prieto et al. (2004)Solar centre-to-limb variation of OI lines
Practical implementation I
“Curves-of-growth” from UV-NIR:
3200 FeI lines107 FeII lines
ΔNLTE
Teff=6500Klog(g)=4.0ξ=2km/s
Lind et al. (2012)
Practical implementation II
Pre-computed departure coefficients NLTE synthesis
T. Nordlander
FeI NLTE grid
Lind et al. (2012)
Application : metal-poor stars
Ruchti et al. (2012)
LTE NLTE+PHOT
Application : metal-poor stars
LTE NLTE+PHOT
Serenelli et al. (2013)
3D (LTE/NLTE)
Is it really necessary?
Is it safe?
Stagger grid
Magic et al. 2014
Abundance patterns
3D
N-LTE
Keller et al. (2014)
Dashed –200 Msun PISNSolid – 60Msun fallback
Worst-case scenario III
Li isotopic abundances
Asplund et al. 2006Lind et al. 2013
3DN-LTE
Observational tests: the Sun
Pereira et al. 2013
“We confronted the models with observational diagnostics of the [solar] temperature profile: continuum centre-to-limb variations (CLVs), absolute continuum fluxes, and the wings of hydrogen lines. We also tested the 3D models for the intensity distribution of the granulation and spectral line shapes. ”
“We conclude that the 3D hydrodynamical model is superior to any of the tested 1D models.”
Observational tests: low [Fe/H]
Klevas et al. 2013
FeI line assymmetriesin the metal-poor giant HD122563
1.5/3D + NLTE
LiI : Asplund et al. 2003, Sbordone et al. 2010
OI, FeI : Shchukina et al. 2005
OI : Pereira et al. 2010, Prakapavičius et al. 2013
LiI, NaI, CaI : Lind et al. 2013
Ways forward
Model LTE/NLTE Time Performance
1D LTE Seconds
1D NLTE Minutes (seconds using interpolation)
3D LTE Hours
3D NLTE Days The ultimate goal, reference point
<3D> LTE Seconds
<3D> NLTE Minutes (seconds using interpolation)
Mg b in a VMP SG
1D LTE1D NLTE<3D> LTE<3D> NLTE
HD140283
Teff=5780Klog(g)=3.7[Fe/H]=-2.4
“No” free parameters!
Yeisson Osorio
Ca in a VMP dwarf
LTE NLTE1D<3D> 3D
HD19445Teff=6000Klog(g)=4.5[Fe/H]=-2.0
Ca in a VMP dwarf
LTE NLTE1D<3D> 3D
HD19445Teff=6000Klog(g)=4.5[Fe/H]=-2.0
Start ? Goal
Bullets: Optical CaI linesSquares: NIR CaII triplet
Ca in a EMP TO
G64-12Teff=6430Klog(g)=4.0[Fe/H]=-3.0
Start ? Goal
Bullets: Optical CaI linesSquares: NIR CaII triplet
Ca in a EMP TO
Start ? Goal
Bullets: Optical CaI linesSquares: NIR CaII triplet
Ca in a EMP TO
Start ? Goal
Bullets: Optical CaI linesSquares: NIR CaII triplet
Ca in a EMP TO
Start ? Goal
Bullets: Optical CaI linesSquares: NIR CaII triplet
Ca in a EMP TO
Ways forward
Model LTE/NLTE Time Performance
1D LTE Seconds Varied
1D NLTE Minutes (seconds using interpolation)
Improves for ANo change for B
3D LTE Hours May worsen for AImproves for B
3D NLTE Days The ultimate goal, reference point
<3D> LTE Seconds May worsen for AImproves for B
<3D> NLTE Minutes (seconds using interpolation)
Improves for AImproves for B
A : NLTE-sensitive, B : not NLTE-sensitive