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**Martin Asplund, Paul Barklem, Andrey Belyaev, Maria Bergemann,**

3D and NLTE analysis for large stellar surveys Karin Lind Uppsala University, Sweden Martin Asplund, Paul Barklem, Andrey Belyaev, Maria Bergemann, Remo Collet, Zazralt Magic, Anna Marino, Jorge Meléndez, Yeisson Osorio

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**Outline Introduction 1D LTE/NLTE Worst-case scenarios Recent progress**

Calibration techniques Practical implementation Applications 3D LTE/NLTE Observational tests Mg : 1D/<3D>/LTE/NLTE Ca : 1D/<3D>/3D/LTE/NLTE

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**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

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**Methods Model atmosphere Detailed rad. Transfer**

1D/<3D>/3D LTE D/3D LTE/NLTE R. Collet

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NLTE line formation

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(1D) N- Is it really necessary? Is it safe?

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**Worst-case scenario I NaD lines in metal-poor horisontal branch stars**

Lind et al. 2011, Marino et al. 2011 B-I

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**Worst-case scenario II**

OI 777nm triplet at very low metallicities LTE trend Fabbian et al. 2009

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**Input data for NLTE analysis**

Energy levels + oscillator strengths + photo-ionization cross sections Red boxes : have sufficient(?) data Blue boxes : missing e.g. QM photo-ionisation, but NLTE still attempted

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**Input data for NLTE analysis**

Blue boxes : QM hydrogen collisions exist or will exist

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**Input data for NLTE analysis**

Most important free parameter in NLTE modelling of Fe is FeI+HI collisional cross-section Black – LTE Blue – NLTE with no hydrogen collisions Solar neighborhood MDF Halo MDF [X/Fe] vs [Fe/H]

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**Calibration techniques: ionisation balance**

Korn et al. 2003 FeI/FeII ionisation equilibrium calibrated using Hipparcos gravities S(H)=3

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**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

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**Calibration techniques: CLV**

Allende Prieto et al. (2004) Solar centre-to-limb variation of OI lines

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**Practical implementation I**

“Curves-of-growth” from UV-NIR: 3200 FeI lines 107 FeII lines Teff=6500K log(g)=4.0 ξ=2km/s ΔNLTE Lind et al. (2012)

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**Practical implementation II**

Pre-computed departure coefficients NLTE synthesis T. Nordlander

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FeI NLTE grid Lind et al. (2012)

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**Application : metal-poor stars**

LTE NLTE +PHOT Ruchti et al. (2012)

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**Application : metal-poor stars**

LTE NLTE+PHOT Serenelli et al. (2013)

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3D (LTE/NLTE) Is it really necessary? Is it safe?

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Stagger grid Magic et al. 2014

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**Abundance patterns 3D N-LTE Keller et al. (2014) Dashed –200 Msun PISN**

Solid – 60Msun fallback 3D N-LTE

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**Worst-case scenario III**

Li isotopic abundances 3D N-LTE Lind et al. 2013 Asplund et al. 2006

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**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.”

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**Observational tests: low [Fe/H]**

Klevas et al. 2013 FeI line assymmetries in the metal-poor giant HD122563

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**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

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**Ways forward Model LTE/NLTE Time Performance 1D LTE Seconds NLTE**

Minutes (seconds using interpolation) 3D Hours Days The ultimate goal, reference point <3D>

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**Mg b in a VMP SG 1D LTE 1D NLTE <3D> LTE <3D> NLTE**

“No” free parameters! HD140283 Teff=5780K log(g)=3.7 [Fe/H]=-2.4 1D LTE 1D NLTE <3D> LTE <3D> NLTE Yeisson Osorio

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**Ca in a VMP dwarf LTE 1D 3D <3D> NLTE HD19445 Teff=6000K**

log(g)=4.5 [Fe/H]=-2.0

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**Ca in a VMP dwarf LTE 1D 3D <3D> NLTE HD19445 Teff=6000K**

log(g)=4.5 [Fe/H]=-2.0

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**Ca in a EMP TO Start ? Goal G64-12 Teff=6430K log(g)=4.0 [Fe/H]=-3.0**

Bullets: Optical CaI lines Squares: NIR CaII triplet

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**Ca in a EMP TO Start ? Goal Bullets: Optical CaI lines**

Squares: NIR CaII triplet

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**Ca in a EMP TO Start ? Goal Bullets: Optical CaI lines**

Squares: NIR CaII triplet

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**Ca in a EMP TO Start ? Goal Bullets: Optical CaI lines**

Squares: NIR CaII triplet

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**Ca in a EMP TO Start ? Goal Bullets: Optical CaI lines**

Squares: NIR CaII triplet

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**Ways forward A : NLTE-sensitive, B : not NLTE-sensitive Model LTE/NLTE**

Time Performance 1D LTE Seconds Varied NLTE Minutes (seconds using interpolation) Improves for A No change for B 3D Hours May worsen for A Improves for B Days The ultimate goal, reference point <3D>

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