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Non-LTE Abundance Analysis of K & Sc in Stars

Explore the chemical evolution of the Milky Way through abundance analysis of odd-Z elements K & Sc in metal-poor stars. Understand LTE vs. NLTE effects on element abundances.

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Non-LTE Abundance Analysis of K & Sc in Stars

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  1. Non-LTE abundance analysis:K & Sc Huawei Zhang Department of Astronomy, School of Physics, Peking University

  2. Collaborators: • Thomas Gehren (LMU) • Keith Butler (LMU) • Shi Jianrong (NAOC) • Zhao Gang (NAOC)

  3. 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.

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

  5. 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.

  6. 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.

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

  8. K & Sc NLTE model K Sc

  9. K lines: LTE vs. NLTE KI: 7698

  10. 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).

  11. Potassium results: metal-poor starsZhang et al., 2006, A&A, 457, 645 • 58 metal-poor stars • DSAZ FOCES • R ~ 40000 • S/N ~ 100-200

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

  13. Potassium results: metal-poor starsZhang et al., 2006, A&A, 457, 645 Samland(1998) Goswami & Prantzos (2000) Timmes et al. (1995)

  14. Scandium results: the SunZhang et al., 2008,A&A, 481, 489 NLTE LTE Sc I 5671 LTE NLTE Sc II 5526

  15. LTE result: Sc II • Sc I: 2.90±0.09 • Sc II: 3.10±0.05 Sc I

  16. 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

  17. Scandium results: metal-poor starsZhang et al., 2008,in preparation [Sc/Fe] ~ [Fe/H] Thick disk Halo Thin disk

  18. Thank You !

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