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化学組成に刻まれた Ia 型超新星の多様性

辻本拓司 ( 国立天文台 ). 化学組成に刻まれた Ia 型超新星の多様性. Talk Outline.  chemical imprint on stars of supernova nucleosynthesis in general, the issue about Type II supernovae  prompt Type Ia supernovae  the origin of stars with a very low [Mg/Fe]

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化学組成に刻まれた Ia 型超新星の多様性

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  1. 辻本拓司 (国立天文台) 化学組成に刻まれたIa型超新星の多様性 Talk Outline chemical imprint on stars of supernova nucleosynthesis in general, the issue about Type II supernovae prompt Type Ia supernovae the origin of stars with a very low [Mg/Fe] the presence of subclass of Type Ia supernovae which yield very low Fe-group elements (Cr, Mn, Ni) 超新星と超新星残骸の融合研究会, １０月１５−１７日 at NAOJ

  2. Chemical abundance studies for extremely-metal poor stars Galactic halo stars -4<[Fe/H]<-1 no contamination from SNeIa pure SN II origin McWilliamet al. 1995 metal-rich halo stars -2.5<[Fe/H]<-1 assembly of SNe II Cayrel et al. 2004 metal-poor halo stars [Fe/H]<-2.5 Yong et al. 2012 individual SN II

  3. Interpretation of chemical composition of extremely metal-poor stars reflection of nucleosynthesisin individual supernovae Audouze & Silk 1995 Shigeyama & TT 1998 Nakamura et al. 1999 Umeda & Nomoto 2002 based on the assumption that stars are born from each supernova remnant Shigeyama & TT 1998 X,Y:supernova yield Nakamura et al. 1999 [X/Y] 0 [Y/H] TT & Bekki 2011 Shigeyama & TT 1998

  4. Delay Time Distribution (DTD) of SNeIa tIa~tGW a4 fsep a-1 Ia型超新星の寿命は短かった observed results from SN Ia surveys for extragalaxies theoretical models double-degenerate scenario Young progenitors for SNeIa are dominant (Mannucci et al. 2006; Sullivan et al. 2006) Totani et al. 2008 Kirby et al. 2011 single-degenerate scenario (Totani et al. 2008; Maoz et al. 2010) Hachisu et al. 2008 about 70% of SNeIa explodes with a time delay within 1 Gyr a significant impact on Galactic chemical evolution

  5. Drastic change in typical timescale of SN Ia progenitors ~1 Gyr ~ 0.1Gyr imply Toomre diagram T=(U2+V2)0.5 break in [a/Fe] among solar neighborhood stars apply Venn et al. 2004 Galactic stars are now well kinematically separated. -1 [Fe/H] Pagel & Tautvaisiene 1995 thin disk no break no high a/Fe stars no low Fe/H stars Yoshii et al. 1996 thick disk the presence of break! DTD discussion on a/Fe break should be assessed by comparing the modeled chemical feature of the thick disk with the corresponding observed one.

  6. Globular cluster with [Mg/Fe]=-0.9±0.3 in the LMC NGC 1718 Al-Mg anticorrelation in GCs [X/Fe] in SN II age ~2Gyr, [Fe/H]=-0.7 [Mg/Fe]=-0.9±0.3 (Colucci et al. 2012) TT & Bekki 2012 Kobayashi et al. 2006 Sneden et al. 2004 other samples in the Carina dSph galaxy Such an extremely low ratio (≤-0.6) is outside any observed Al-Mg anticorrelations (>-0.3) as well as by the prediction from nucleosynthesis calculations on any SNe II (>-0.2). Lemasle et al. 2012 Nucleosynthesis in SNeIa gives [Mg/Fe]≈-1.5. (Iwamoto et al. 1999) Likely, its birth place is the ejecta of SNe Ia.

  7. SN Ia-like abundances of Fe-peak elements AGB-like abundances of light-odd elements WDD1, WDD2 model from Iwamoto et al. 1999 Colucci et al. 2012 Light odd-elements, Na and Al, are synthesized in AGB stars, with a production peak at a ~5 Msun AGB star (e.g., Karakas et al. 2007). Since the lifetime of 5 Msun star is ~0.1 Gyr, which is nearly equivalent to the major delay time for prompt SNeIa, the ejecta of prompt SNeIa might be unavoidably contaminated by the release of Na and Al from mass-losing AGB stars. predicted values: [Na/Fe]=-0.03 [Al/Fe]=+0.15 TT & Bekki 2012

  8. Giant HI holes in the LMC However, in an already chemically enriched ISM, e.g., with [Fe/H]≈-0.5, relic of nucleosynthesis in individual SNe is hardly imprinted in stellar abundances. SN Ia explosion in a low metallicity ISM is crucial. Kim et al. 1999 1.At the beginning, a star cluster with the mass of ~4x104Msun is formed. 2.Subsequently, a busting SNe II explosions expel the surrounding ISM of this cluster, and make a HI hole. 3.Onto this HI hole, a gas disrupted from the SMC with a metallicity of [Fe/H]<-1.3 accretes. 4.Sequential prompt SNeIa start to explode and the multiple ejecta of SNeIa merge and mix with the new ISM supplied by the accreting metal-poor gas. Finally, NGC 1718 is formed from its mixed gas. LMC-SMC interaction Diaz & Bekki 2012

  9. A very low [Mg/Fe] star with detailed abundances in the Carina dSph very low [Fe-group/Fe] ratios Car-612 Koch et al. 2008 [Mg/Fe]=-0.9±0.09 Venn et al. 2012

  10. low [Fe-group/Fe] ratios in dwarf galaxies FornaxdSph LMC Letarte et al. 2010 Fornax Sculptor North et al. 2012 Pompeia et al. 2008 Sextans

  11. NGC 1718 prompt SNeIa & slow SNeIa A majority of SNeIa explode promptly after the bursting explosions of SNe II (prompt SNeIa), and the rest gradually emerge with a long interval of Gyrs (slow SNeIa). Car-612 - promptSNeIa - The ejecta of prompt SNeIa, which synthesize Fe-group elements more efficiently as already predicted in the existing SN models, can easily escape from the gravitational potential, if it is shallow, owing to an inactive cooling in the low-density ISM after the bursting SN II explosions. - slow SNeIa - Nucleosynthesis of slow SNeIa is characteristic of low [Fe-group/Fe] ratios as observed in Car-612. ≥ In the models, tdelay 1 Gyr is assumed. ≤ TT & Shigeyama 2012

  12. solving the [Mg/Ca] problem in dwarf galaxies DSph stars exhibit very high [Mg/Ca] ratios. dSph LMC Car-612 NGC 1718 MW Koch 2008 The Mg yield of SN Ia is completely negligible as compared with that of SN II. If slow SNeIa yield a low Ca abundance like Fe-group elements, [Ca/Fe] will become lower than [Mg/Fe]. TT & Shigeyama 2012

  13. New Model for SN Ia explosion in the scheme of SNeIa resulting from a 0.8+0.6 M⊙ white dwarf merger (0.6+0.4 M⊙ to 1.1+0.6 M⊙ models) the explosion of a WD with the mass 0.8 M⊙ accreting 0.6 M⊙ matter at the mass accretion rate of 0.07 M⊙ s-1 a dim SN Ia after spending more than 1 Gyr from the birth subluminousSNeIa already predicted as a result of the merger of two WDs(Pakmor et al. 2010, 2011) TT & Shigeyama 2012

  14. Summary Chemical feature of stars implies the diversity of SNeIa yielding different nucleosynthesisproducts. ,motivated by two stellar relics (NGC 1718 & Car-612) We discover a subclass of SNeIa which releases low abundances of Fe-group elementswith a long timescale and leaves little relics in the chemical abundances in the Galaxy. In dwarf galaxies like the LMC, owing to the difficulty in trapping the ejecta from prompt SNeIa that synthesize a large amount of Fe-group elements and explode in burst, the proposed SNeIa characterize the chemical feature of a late evolution, which leads to a large scatter in [Cr,Mn,Ni/Fe]. We need ✓determination of detailed elemental abundances for more stars exhibiting very low [Mg/Fe] ✓three-dimensional simulations for SN Ianucleosynthesis

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