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 )  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 超新星と超新星残骸の融合研究会, １０月１５ − １７日 at NAOJ Talk Outline (Cr, Mn, Ni)

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

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

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

Drastic change in typical timescale of SN Ia progenitors ~1 Gyr ~ 0.1Gyr [Fe/H] Pagel & Tautvaisiene 1995 break in [a/Fe] among solar neighborhood stars Yoshii et al Toomre diagram Venn et al thin disk no break no high  /Fe stars no low Fe/H stars thick disk the presence of break! Galactic stars are now well kinematically separated. imply apply DTD discussion on  /Fe break should be assessed by comparing the modeled chemical feature of the thick disk with the corresponding observed one. T=(U 2 +V 2 ) 0.5

Lemasle et al Globular cluster with [Mg/Fe]=-0.9±0.3 in the LMC 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). NGC 1718 age ~2Gyr, [Fe/H]=-0.7 [Mg/Fe]=-0.9±0.3 (Colucci et al. 2012) TT & Bekki 2012 Likely, its birth place is the ejecta of SNe Ia. other samples in the Carina dSph galaxy Sneden et al Kobayashi et al Al-Mg anticorrelation in GCs [X/Fe] in SN II Nucleosynthesis in SNe Ia gives [Mg/Fe]≈-1.5. (Iwamoto et al. 1999)

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

Diaz & Bekki 2012 Kim et al Giant HI holes in the LMC 1.At the beginning, a star cluster with the mass of ~4x10 4 M sun 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 SNe Ia start to explode and the multiple ejecta of SNe Ia 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 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.

Koch et al Venn et al A very low [Mg/Fe] star with detailed abundances in the Carina dSph Car-612 [Mg/Fe]=-0.9±0.09 very low [Fe-group/Fe] ratios NGC1718 Car-612 [Cr/Fe] [Mn/Fe] [Co/Fe] <-0.86 [Ni/Fe] [Zn/Fe] -0.83

Pompeia et al Letarte et al North et al low [Fe-group/Fe] ratios in dwarf galaxies Fornax Sculptor Sextans LMC Fornax dSph

A majority of SNe Ia explode promptly after the bursting explosions of SNe II (prompt SNe Ia), and the rest gradually emerge with a long interval of Gyrs (slow SNe Ia). prompt SNe Ia & slow SNe Ia Nucleosynthesis of slow SNe Ia is characteristic of low [Fe-group/Fe] ratios as observed in Car The ejecta of prompt SNe Ia, 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 SNe Ia - - prompt SNe Ia - TT & Shigeyama 2012 NGC 1718 Car-612 In the models, t delay 1 Gyr is assumed. ≥ ≤

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

New Model for SN Ia explosion typeFeCrMnNi comment Slow SN Ia x x x10 -3 nucleosynthesis caclulation (this study) 2.5x x x10 -3 prediction from chemical evolution prompt SN Ia x x x10 -2 WDD2 model in Iwamoto et al in the scheme of SNe Ia resulting from a M ⊙ white dwarf merger 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 already predicted as a result of the merger of two WDs (Pakmor et al. 2010, 2011) TT & Shigeyama 2012 subluminous SNe Ia ( M ⊙ to M ⊙ models)

Summary  We discover a subclass of SNe Ia which releases low abundances of Fe-group elements with 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 SNe Ia that synthesize a large amount of Fe-group elements and explode in burst, the proposed SNe Ia characterize the chemical feature of a late evolution, which leads to a large scatter in [Cr,Mn,Ni/Fe]. ✓ determination of detailed elemental abundances for more stars exhibiting very low [Mg/Fe] ✓ three-dimensional simulations for SN Ia nucleosynthesis We need Chemical feature of stars implies the diversity of SNe Ia yielding different nucleosynthesis products., motivated by two stellar relics (NGC 1718 & Car-612)