Non-LTE abundance analysis: K

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Non-LTE abundance analysisK Sc

• Huawei Zhang
• Department of Astronomy,
• School of Physics, Peking University

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Collaborators

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

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• The history of the Galaxy is written in the
  evolution of its composition.
• The low mass unevolved stars have long lifetimes,
  some of them have comparable to the age of the
  Galaxy.
• Their atmospheric compositions have preserved
  much of their natal interstellar clouds.

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• The determination of the element abundances in
  stars of different metallicities is important for
  understanding the chemical evolution of the Milky
  way.

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Abundance analysis

• Still today, the vast majority of abundance
  analyses of late-type stars rely on the
  assumption of local thermodynamic equilibrium
  (LTE).
• Departures from LTE are common place and often
  quite important.

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LTE vs. NLTE

• LTE The level populations can be directly
  computed from the local gas temperature by the
  use of the Boltzmann and Saha distributions.
• NLTE These rate equations must be solved
  simultaneously with radiative transfer equation
  for all relevant frequencies.

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• K (Z19) and Sc (Z21) are odd-Z elements.

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K Sc NLTE model
K
Sc
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K lines LTE vs. NLTE
KI 7698
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Potassium results the Sun
Zhang et al., 2006, AA, 453, 723

• Average solar potassium abundance
• log ??(K) 5.120.03
• Corresponds to the meteoritic value (Grevesse
  Sauval, 1998).

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Potassium results metal-poor stars Zhang et
al., 2006, AA, 457, 645

• 58 metal-poor stars
• DSAZ FOCES
• R 40000
• S/N 100-200

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• The NLTE corrections for metal-poor stars are
  negative and the average of -0.40 dex.

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Potassium results metal-poor stars Zhang et
al., 2006, AA, 457, 645
Samland(1998)
Goswami Prantzos (2000)
Timmes et al. (1995)
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Scandium results the Sun
Zhang et al., 2008, AA, 481, 489
NLTE
LTE
Sc I 5671
LTE
NLTE
Sc II 5526
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LTE result
Sc II

• Sc I 2.900.09
• Sc II 3.100.05

Sc I
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NLTE result

• Sc I 3.080.05
• Sc II 3.070.04

Sc I
Sc II
Sc I
Sc II
Sc II
Sc I
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Scandium results metal-poor stars
Zhang et al., 2008, in preparation
Sc/Fe Fe/H
Thick disk
Halo
Thin disk
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Thank You !