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Non-LTE abundance analysis: K & Sc. Huawei Zhang Department of Astronomy, School of Physics, Peking University. Collaborators:. Thomas Gehren (LMU) Keith Butler (LMU) Shi Jianrong (NAOC) Zhao Gang (NAOC). The history of the Galaxy is written in the evolution of its composition .

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non lte abundance analysis k sc

Non-LTE abundance analysis:K & Sc

Huawei Zhang

Department of Astronomy,

School of Physics, Peking University

slide2

Collaborators:

  • Thomas Gehren (LMU)
  • Keith Butler (LMU)
  • Shi Jianrong (NAOC)
  • Zhao Gang (NAOC)
slide3
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.
slide4
The determination of the element abundances in stars of different metallicities is important for understanding the chemical evolution of the Milky way.
abundance analysis
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.
lte vs nlte
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.
potassium results the sun zhang et al 2006 a a 453 723
Potassium results: the SunZhang et al., 2006,A&A, 453, 723
  • Average solar potassium abundance:

log (K) = 5.12±0.03

  • Corresponds to the meteoritic value (Grevesse & Sauval, 1998).
potassium results metal poor stars zhang et al 2006 a a 457 645
Potassium results: metal-poor starsZhang et al., 2006, A&A, 457, 645
  • 58 metal-poor stars
  • DSAZ FOCES
  • R ~ 40000
  • S/N ~ 100-200
potassium results metal poor stars zhang et al 2006 a a 457 6451
Potassium results: metal-poor starsZhang et al., 2006, A&A, 457, 645

Samland(1998)

Goswami & Prantzos (2000)

Timmes et al. (1995)

slide15

LTE result:

Sc II

  • Sc I: 2.90±0.09
  • Sc II: 3.10±0.05

Sc I

slide16

NLTE result:

Sc I

  • Sc I: 3.08±0.05
  • Sc II: 3.07±0.04

Sc II

Sc I

Sc II

Sc II

Sc I

scandium results metal poor stars zhang et al 2008 in preparation
Scandium results: metal-poor starsZhang et al., 2008,in preparation

[Sc/Fe] ~ [Fe/H]

Thick disk

Halo

Thin disk

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