爆燃Ia型超新星爆発時におけるダスト形成
野沢 貴也
東京大学数物連携宇宙研究機構（ＩＰＭＵ）
共同研究者
前田啓一(IPMU), 野本憲一 (IPMU/東大), 小笹隆司(北大)1-1. Introduction○ Type Ia SNe・ thermonuclear explosion of a C+O WD withthe mass close to Chandrasekhar limit－ subsonic deflagration?
－ (delayed) detonation?

・ eject a significant amount of Fe-peak andintermediate elements such as Si, S, and Ca➔ play a role in the cosmic chemical evolution

・ abundant metals in SNe Ia ➔ dust can form?
Type II SN : 0.1-1 Msun (from theories)> 10-4 Msun (from observations)1-2. Dust in Type Ia SNe○ Dust formation in SNe Ia－ SNe Ia may form a significant amount of Fe grains(e.g. Dwek 1998)－ presolar SiC grains in meteorites may be producedin SNe Ia to account for their isotopic sinatures(Clayton et al. 1997)－ no clear decrease of light curve by dust absorption－ no IR dust emission as well as CO molecules
SN 2003hv, SN 2005bv at 100-300 days
(Gerardy et al. 2007)－ no signature of ejecta-dust in Tycho SNR(e.g., Douvion et al. 2001)

1-3. Aim of our study
・ What is the difference in formation process ofdust between SNe Ia and SNe II?
・ Is it possible for dust grains to condense in theejecta of Type Ia SN?

・ chemical composition, size, and mass of
newly formed dust
・ dependence of dust formation process ontypes of SNe

・ implication on nuclear burning in SNe Ia

2-1. Calculation of dust formation○ nucleation and grain growth theory (Nozawa et al. 2003)
steady-state nucleation rate
2grain growth rate

・ key species:a gas species with the least collision frequency among
reactants・ sticking probability; αsj = 1, 0.1, 0.01
・ Tdust = Tgas (dust temperature is the same as that of gas)

2-2. Dust formation calculation for SN Ia○ Type Ia SN modelW7 model (C-deflagration)(Nomoto et al. 1984)－ Meje = 1.32 Msun

－ E51 = 1.3－ M(56Ni) = 0.56 Msun
－ onion-like composition(no mixing of elements)－ formation efficiency of
CO and SiO ➔ 0 or 1
C / O > 1 ➔ all O atoms are locked into CO
C / O < 1 ➔ all C atoms are locked into CO
Si / O < 1 ➔ all Si atoms are locked into SiO

3-1. Condensation time of dustwith moleculeswith no molecules

・ Various species of dust condense in each layer
・ species of dust depends on formation of molecules

・ condensation time of dust : 100-300 days

3-2. Average radii of dustwith moleculeswith no molecules

・ average radius of Fe and Ni : ~ 0.01 μm
・ average radius of other dust species : < 0.01 μm

because of low density of gas in the expanding ejecta

3-3. Mass of dust formed in SN Ia

・ Total mass of dust formed in SNe Ia : Mdust < 0.13 Msun
・ Fe and SiC grains cannot condense significantly

4-1. Optical depth by dust
Optical depth at 300 daysτ(0.55) ~ 200 at 300 daysτ(0.55) ~ 100 by C grains
τ(0.55) ~ 100 by Si and FeS➔ too high to be consistent
with observations

early formation of dust ➔ 100-300 days
high M(56Ni)➔ ~0.6 Msun
➔ dust evaporates soon after the formation
by strong radiation field in the ejecta?

4-2. Dust temperature

F(r)= L / 4 π r^24-3. Mass of dust survived
Mass of dust formed

There is no evidence that C
has been detected in SN Ia

If we ignore C grains in SN Ia
Mdust ~ 0.03 Msun
τ(0.55) ~ 1 at 300 day

Summary1) Dust formed in the ejecta of SNe Ia・various grain species with average radius : < 0.01 μm
・upper limit of total mass : ~0.1 Msun
2) Strong radiation field in the ejecta of SNe Ia➔ destroy most of FeS and Si but not C and silicate
3) Formation of C grains is inconsistent with observations➔ preexisting C should be burned by nuclear burningabsence of C layer ➔ dust mass : 0.03 Msun4) Newly formed dust grains of < 0.01μm may not be able
to survive the reverse shock due to their small radii(Nozawa et al. to be submitted soon!)