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Non-LTE Abundance Analysis of Potassium and Scandium in Unevolved Low-Mass Stars

This research explores the significance of non-local thermodynamic equilibrium (NLTE) in the abundance analysis of potassium (K) and scandium (Sc) in low-mass, unevolved stars. These stars, with their long lifetimes, retain atmospheric compositions reflective of their natal interstellar clouds. The study emphasizes the departure from LTE in abundance calculations, particularly for metal-poor stars, revealing how NLTE corrections alter the understanding of elemental abundances. Collaborations with experts from institutions like LMU and NAOC highlight the analytical depth of this work in unraveling the Milky Way's chemical evolution.

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Non-LTE Abundance Analysis of Potassium and Scandium in Unevolved Low-Mass 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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