Non-LTE abundance Non-LTE abundance analysis:analysis:K & ScK & Sc

Huawei ZhangHuawei Zhang

Department of Astronomy, Department of Astronomy, School of Physics, Peking UniversitSchool of Physics, Peking Universit

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Collaborators:Collaborators:

• Thomas Gehren (LMU)Thomas Gehren (LMU)• Keith Butler (LMU)Keith Butler (LMU)• Shi Jianrong (NAOC)Shi Jianrong (NAOC)• Zhao Gang (NAOC)Zhao Gang (NAOC)

• The history of the Galaxy is written in thThe history of the Galaxy is written in the evolution of its e evolution of its compositioncomposition..

• The The low mass unevolvedlow mass unevolved stars have long stars have long lifetimes, some of them have comparabllifetimes, some of them have comparable to the age of the Galaxy.e to the age of the Galaxy.

• Their atmospheric compositions have prTheir atmospheric compositions have preserved much of their natal interstellar ceserved much of their natal interstellar clouds. louds.

•The determination of the element abThe determination of the element abundances in stars of different metalliundances in stars of different metallicities is important for understanding cities is important for understanding the the chemical evolutionchemical evolution of the Milky w of the Milky way.ay.

Abundance analysisAbundance analysis

• Still today, the vast majority of abundanStill today, the vast majority of abundance analyses of late-type stars rely on the ce analyses of late-type stars rely on the assumption of local thermodynamic equassumption of local thermodynamic equilibrium (ilibrium (LTELTE). ).

• Departures from LTE are common place Departures from LTE are common place and often quite important.and often quite important.

LTE vs. NLTELTE vs. NLTE

•LTE:LTE: The level populations can be direc The level populations can be directly computed from the local gas tempertly computed from the local gas temperature by the use of the ature by the use of the BoltzmannBoltzmann and and SSahaaha distributions. distributions.

•NLTE:NLTE: These These rate equationsrate equations must be so must be solved simultaneously with radiative translved simultaneously with radiative transfer equation for all relevant frequencies. fer equation for all relevant frequencies.

•K (K (Z=19Z=19) and Sc () and Sc (Z=21)Z=21) are are odd-odd-ZZ elements. elements.

K & Sc NLTE modelK & Sc NLTE model

K

Sc

K lines: LTE vs. NLTE

KI: 7698

Potassium results: Potassium results: the Sunthe Sun Zhang et al., 2006,Zhang et al., 2006, A&A, 453, 723A&A, 453, 723

• Average solar potassium abundance:Average solar potassium abundance:

log log (K) = 5.12±0.03(K) = 5.12±0.03

• Corresponds to the meteoritic value (GrCorresponds to the meteoritic value (Grevesse & Sauval, 1998).evesse & Sauval, 1998).

Potassium results: Potassium results: metal-poor metal-poor starsstars Zhang et al., 2006, A&A, 457, 645Zhang et al., 2006, A&A, 457, 645

• 58 metal-po58 metal-poor starsor stars

• DSAZ FOCESDSAZ FOCES

• R ~ 40000R ~ 40000

• S/N ~ 100-20S/N ~ 100-2000

• The NLTE corThe NLTE corrections for rections for metal-poor smetal-poor stars are tars are neganegativetive and the a and the average of verage of -0.4-0.40 dex0 dex..

Potassium results: Potassium results: metal-poor metal-poor starsstars Zhang et al., 2006, A&A, 457, 645Zhang et al., 2006, A&A, 457, 645

Samland(1998)

Goswami & Prantzos (2000)

Timmes et al. (1995)

Scandium results: Scandium results: the Sunthe Sun Zhang et al., 2008,Zhang et al., 2008, A&A, 481, 489A&A, 481, 489

Sc I 5671

LTE

NLTE

Sc II 5526

NLTELTE

LTE result: LTE result:

• Sc I: Sc I: 2.902.90±0.09±0.09

• Sc II: Sc II: 3.103.10±0.05±0.05

Sc II

Sc I

NLTE result:

• Sc I: 3.08±0.05

• Sc II: 3.07±0.04

Sc II

Sc I

Sc II

Sc ISc I

Sc II

Scandium results: Scandium results: metal-poor metal-poor starsstars Zhang et al., 2008,Zhang et al., 2008, in preparationin preparation

Thick disk

Thin diskHalo

[Sc/Fe] ~ [Fe/H][Sc/Fe] ~ [Fe/H]

Thank You !