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. 1995

Cayrel et al. 2004

Yong et al. 2012

-2.5<[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

€

Msw = 5.1×104 MsunE0

1051 ergs

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

0.97

× n−0.062 Cs

10km s−1

⎛

⎝ ⎜

⎞

⎠ ⎟−9/7

Audouze & Silk 1995Shigeyama & TT 1998Nakamura et al. 1999Umeda & Nomoto 2002

[X/Y

]

[Y/H]0

Shigeyama & TT 1998 Nakam

ura et al. 1999

Shigeyama & TT 1998

TT & B

ekki 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. 2008H

achisu et al. 2008

double-degenerate scenario

single-degenerate scenario

Kirb

y et

al.

2011

theoretical modelsobserved results from SN Ia surveys for extragalaxies

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DTD ∝ tdelay−1 for 0.1Gyr < tdelay <10 Gyr

(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tIa~tGW a4

fsep 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

Yosh

ii et

al.

1996

Toomre diagramVenn et al. 2004

thin disk no break no high a/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 a/Fe break should be assessed by comparing the modeled chemical feature of the thick disk with the corresponding observed one.

-1

T=(U2+V2)0.5

Lemasle et al. 2012

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 1718age ~2Gyr, [Fe/H]=-0.7[Mg/Fe]=-0.9±0.3 (Colucci et al. 2012)

TT & B

ekki 2012

Likely, its birth place is the ejecta of SNe Ia.

other samples in the Carina dSph galaxySneden et al. 2004 Kobayashi et al. 2006

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. 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 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. 1999

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. 1999

Giant HI holes in the LMC

1.At the beginning, a star cluster with the mass of ~4x104 Msun 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 enrichedISM, e.g., with [Fe/H]≈-0.5, relicof nucleosynthesis in individual SNe is hardly imprinted in stellar abundances.

SN Ia explosion in a low 　 metallicity ISM is crucial.

Koch et al. 2008

Venn et al. 2012

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] +0.25 -0.20

[Mn/Fe] -0.05 -0.51

[Co/Fe] <-0.86

[Ni/Fe] +0.09 -0.46

[Zn/Fe] -0.83

Pompeia et al. 2008

Letarte et al. 2010

North et al. 2012

low [Fe-group/Fe] ratios in dwarf galaxies

FornaxSculptor

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-612.

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, tdelay 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

type Fe Cr Mn Ni commentSlow SN Ia 0.41 6.9x10-3 1.1x10-3 7.8x10-3 nucleosynthesis caclulation (this study)

2.5x10-3 1.5x10-3 8.9x10-3 prediction from chemical evolutionprompt SN Ia 0.71 1.7x10-2 7.1x10-3 5.9x10-2 WDD2 model in Iwamoto et al. 1999

in the scheme of SNe Ia resulting from a 0.8+0.6 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

(0.6+0.4 M⊙ to 1.1+0.6 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)