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Near Field Cosmology with Binary ― among extremely metal-poor stars in the Galactic halo　―

Near Field Cosmology with Binary ― among extremely metal-poor stars in the Galactic halo　―. Yutaka Komiya (Tohoku Univ.) Takuma Suda, Asao Habe, Masayui Fujimoto (Hokkaido Univ.). OMEG07 Hokkaido University Dec. 04, 2007. Near Field Cosmology. ?.

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Near Field Cosmology with Binary ― among extremely metal-poor stars in the Galactic halo　―

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  1. Near Field Cosmology with Binary―among extremely metal-poor stars in the Galactic halo　― Yutaka Komiya (Tohoku Univ.) Takuma Suda, Asao Habe, Masayui Fujimoto (Hokkaido Univ.) OMEG07 Hokkaido UniversityDec. 04, 2007

  2. Near Field Cosmology ? • Formation and evolution of stars in the early universe • Nature of first stars and first supernovae • Galaxy formation process WMAP SUBARU • EMP (Extremely Metal-Poor) stars ([Fe/H]≦-2.5)=“Messengers from the early universe” • Stars formed in the proto-galaxy in the early universe. And low massstars still alive near to us.

  3. Chemical evolution Supernova nucleosynthesis Dispersion of supernova yields Changes of the surface abundances of EMP stars Evolution of EMP star Binary mass transfer Accretion of interstellar matter Near Field Cosmology Observations of EMP stars Early universe

  4. ~25% of EMP stars show large C enhancement. (CEMP)They are formed in a binary system. (Komiya et al. 2007) An EMP survivor formed as a secondary component of a binary can be a probe into more massive primary star. Binary H Massive primary evolved to produce C and transfer them onto the low mass secondary through the wind accretion. C,O He H Low mass EMP survivor Massive primary

  5. Initial Mass Function Abundance pattern of CEMP stars Mass of the primary stars IMF of EMP stars Typical mass of EMP stars is ~10 M☉. (EMP survivors are 1/10 low mass component) Most of EMP survivors are secondary companion of binary systems. IMF of primary star IMF of secondary companion mξ(m) AGB⇒WD EMP survivors Supernova 0.1 1 10 100 (M☉ )

  6. Ultra/Hyper metal-poor stars Norris+ (2007) EMP UMP HMP • 3 stars with [Fe/H]<-4.5 • All 3 stars show C enhancement. • Formation scenarios • Pop.III stars with AGB mass transfer + ISM accretion(Suda et al.2004) • Peculiar supernovae (Umeda & Nomoto 2003) • Massive stellar wind (Maynet 2006)

  7. Early Chemical Evolution & Structure Formation To realize the formation and evolution history of EMP stars • Early chemical evolution with • Structure formation • Top heavy IMF • Binary • Accretion of ISM • First star Mini-halos ~106M☉ Galaxies are formed through the merging of the smaller scaled cloud HERMES program (Hierarchical Evolution Researcher by MEtal-poor Stars)

  8. Assumptions • Merging history: Somerville & Kollat (1999) • Mini halos are well mixed, closed boxes. • Supernovae • Fe yield: 0.07 M☉, (stars with 12~50M☉ become Type II SN) • 10M☉(Pair instability supernova ) • Star formation • Constant star formation efficiency : 10-10/yr • IMF • High mass IMF • Equal numbers of binaries and single stars. Mass ratio distribution of binary components n(q)=const.

  9. Result 1. Metallicity Distribution Function Model reproduce cut-off around [Fe/H]~-4. ⇒hierarchical structure formation Result of our calculation. Pop.III stars >100 stars predicted ⇒a fraction of low mass star is much smaller for Pop.III. Obserbed number districution Z=0

  10. Result 2. Supernova progenitors Distribution of stars formed in gas polluted by 1, 2, 5, 10 SNe. Z=0

  11. Results 3. Pair-Instability Super Novae Case I Assumptions PISNe blow out all gas and metal in the minihalo. Case I: PISNe are formed in all minihalos Case II: [Fe/H]<-5.5 :PISN, [Fe/H]>-5.5 : Type II SN Case II Results Case I: ⇒ metal overproduction Case II: ⇒Many HMP stars

  12. Surface pollution • Accretion of interstellar matter change surface abundance of Pop.III or UMP star. Assumptions • Bondi accretion (Mini-halo ⇒ low V ⇒high accretion rate) • Case I: Stars move with virial velocity • ρ=ρvir=ρc(z)ΩbΔc, V=Vvir (minihalovirial velosity） • m=m2 (Bondi radius of secondary star) • Case II． Gas & stars are concentrated to center of mini-halos • ρ=ρvir×(Tvir/200K), V=Vvir ×(200K/Tvir)1/2, • Halo merge after • m=m1+m2 (Bondi radius of bianary system)

  13. Result 4.1 ISM accretion(case I) Accretion rate: <10-14~-15M☉/yrTotal: ~10-7~-8 M☉ Main sequence (Mscz=0.003 M☉ )⇒ [Fe/H]~-7 Giant (Mscz=0.3M☉ )⇒[Fe/H]~-9 (Mscz: mass of surface convection zone) dwarfs giants Z=0

  14. Result 4.1ISM accretion (case II) Accretion rate : ~10-9~-12M☉/yr giants dwarfs Pop.III star become [Fe/H]~-5 (giants) ⇒HMP, UMP star? Z=0

  15. Summary • EMP stars have undergone some changes in the surface abundance • Many EMP survivors affected by binary mass transfer. • IMF of EMP star ([Fe/H]≦-2.5) is high mass. • Interstellar pollution is important for HMP/UMP stars. • Chemical evolution + structure formation • Formation process of our Galaxy affect metallicity distribution of EMP stars. • Most of Pop.III stars may not become pair-instability supernovae. • UMP/HMP stars are possibly Pop.III survivors

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