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Takuma Suda 1 , Takanori Nishimura 1 , Nobuyuki Iwamoto 2 , Masayuki Aikawa 3 ,

New Trends of Physics 2005, Hokkaido University, March 1. Nucleosynthesis in Extremely Metal-Poor Stars of Low and Intermediate Mass and Identification of Population III Survivors. Takuma Suda 1 , Takanori Nishimura 1 , Nobuyuki Iwamoto 2 , Masayuki Aikawa 3 , Masayuki Y. Fujimoto 1 and

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Takuma Suda 1 , Takanori Nishimura 1 , Nobuyuki Iwamoto 2 , Masayuki Aikawa 3 ,

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  1. New Trends of Physics 2005, Hokkaido University, March 1 Nucleosynthesis in Extremely Metal-Poor Stars of Low and Intermediate Mass and Identification of Population III Survivors Takuma Suda1, Takanori Nishimura1, Nobuyuki Iwamoto2, Masayuki Aikawa3, Masayuki Y. Fujimoto1 and Icko Iben Jr.4 1 : Hokkaido University 2 : Japan Atomic Energy Research Institute 3 : Universite Libre de Buruxelles 4 : University of Illinois

  2. Topics • Characteristics of Extremely Metal-Poor Stars • AGB Evolution of Extremely Metal-Poor Stars • Nucleosynthesis in Ultra Metal-Poor Stars

  3. 1. Characteristics of Extremely Metal-Poor Stars

  4. Extremely Metal-Poor (Iron-Poor) Stars • EMP : Extremely Metal-Poor stars • [Fe/H] < -3 : ~100 stars • [Fe/H] < -3.5 : ~10 stars • No stars for - 5 < [Fe/H] < - 4 • 2 stars below [Fe/H] = - 5 UMP : Ultra Metal-Poor stars

  5. Motivations We aim to … • Get information about the chemical history of the early universe. • Provide the prescription to discuss the effect of internal/external pollution on the surface chemical composition of stars during their long lives. • Identify the first generation stars

  6. Characteristics in EMP • Large fraction (25%) of carbon stars (C/O > 1) compared with the Population I & II stars (a few %) • Large scattering in the abundances of s-process elements around [Fe/H] ~ -3 2 2 1 [Ba/Fe] [C/Fe] 0 0 -1 -2 -2 -4 -3 -1 0 -3.5 -3 -4 -2.5 -2 [Fe/H] [Fe/H] Aoki et al.(2002)

  7. The Explanation for the Origin of UMP • Approach from the origin of elements • Origin of light alpha elements, N, and Na • Origin of s-process elements

  8. 2. AGB Evolution of Extremely Metal-Poor Stars

  9. He C+O He AGB Evolutionof EMP He-Flash Convection H+He Surface Convection

  10. Bottom of surface convection Bottom of Hydrogen burning shell He flash driven convection 12C(p,γ)13N(e+ν)13C(α,n)16O & Neutron Capture Nucleosynthesis He-Flash Driven Deep Mixing in EMP Hydrogen Mixing (only for [Fe/H] < -2.5) Mr time

  11. Dredge-up of n-capture elements Dredge-up of C, N H mixing H mixing storage of n-capture elements 13C mixing He-FDDM in EMP (2) Helium shell flash phase 3rd dredge-up He-FDDM H-Flash Convection Surface convection Mr : mass coordinate He/H interface He-Flash Convection With/Without splitting the convection Time

  12. 3. Nucleosynthesis in Ultra Metal-Poor Stars

  13. 35S 32S 33S 34S Reaction Network 32P 33P 28P 29P 30P 31P 27Si 28Si 29Si 30Si 25Al 26Al 27Al 28Al 29Al 22Mg 23Mg 24Mg 25Mg 26Mg 20Na 21Na 22Na 23Na 18Ne 19Ne 20Ne 21Ne 22Ne 17F 18F 19F Z 14O 15O 16O 17O 18O 12N 13N 14N 15N 65 isotopes 11C 12C 13C 14C n-capture p-capture α-capture βdecay Bao et al. (2000) 8B 9B 10B 11B NACRE Caughlan & Fowler (1988) 7Be 8Be 9Be 6Li 7Li Tables of Isotopes 3He 4He 6He developed by M. Aikawa and T. Nishimura A 1H 2H 3H n

  14. Extended Network • 926 nuclei and ~1700 reactions (mainly n-capture and beta decay) are computed with the program developed by N. Iwamoto. • Change of composition is determined by giving abundance of 34S and neutron density for each time step.

  15. Initial Models of He-Shell Flash One zone approximation of He-shell flashes 8.5 (Description : Aikawa, Fujimoto, Kato 2001) Input Parameters Z=0, 10-5.4Z☉ 13C/12C=0.001-0.03 τmix=108-1011sec log T 8.15 102 Time (sec) 1016

  16. Abundance Distribution normalized by carbon abundance 13C/12C=0.02 dtmix=1011(sec) 13C/12C=0.001 dtmix=1011(sec) Magic number of neutron (50,82,126) Pb Sr Ba [Sr/Ba] < -0.5

  17. Conclusions • Final abundances of light elements (Na, Mg, Al) depend on the degree of mixing and these are well reproduced for HE0107, HE1327. • Sr of HE1327 may have another source. • Initial metals effectively absorb neutrons and are converted into Pb. • The determination of Pb abundance is crucial for the identification of Population III survivors.

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