Cas A 超新星残骸中のダストの進化と熱放射
野沢 貴也
東京大学数物連携宇宙研究機構（ＩＰＭＵ）
共同研究者
小笹 隆司(北大), 冨永望 (国立天文台), 前田啓一(IPMU),
梅田秀之 (東大), 野本憲一 (IPMU/東大)1-1. Introduction○ Dust in SNRs
・ CCSNe are important sources of dust?
－ formation of dust in the ejecta of SNe－ destruction of dust by the reverse shock➔ What kind and how much amount of dust aresupplied by CCSNe?

・ physical processes of dust in shocked gas－ erosion by sputtering and collisional heating・ IR thermal emission from shock-heated dust
➔ structure of circumstellar medium and mass-loss
history of progenitor staryoung remnants of CCSNe!

1-2. Cassiopeia A SNR○ Cas A SNR－ age: ~340 yr (Thorstensen et al. 2001)－ distance: d=3.4 kpc (Reed et al. 1995)－ shock radius
forward shock : ~150” (~2.5 pc)
reverse shock : ~100” (~1.7 pc)➔ dM/dt ~ 2x10-5 (vw/10 km/s) Msun/yr(Chevalier & Oishi 2003)－ oxygen-rich SNR
dense O-rich fast-moving knots (O, Ar, S, Si, Fe …)
thermal emission from ejecta-dust➔ Mdust = 0.02-0.054 Msun (Rho et al. 2008)－ SN type : Type IIb (Mstar=15-20 Msun)(Usuda-san’s talk; Krause et al. 2008)

1-3. Aim of our study
・ Formation of dust in the ejecta of Type IIb SN➔ composition, size, and mass of newly formed dust
➔ dependence of dust formation process on typesof SNe (on the thickness of H envelope)・ Evolution of dust in shocked gas within the SNR➔ What fraction of newly formed dust can survive
and is injected into the ISM?

・ Thermal emission from shock-heated dust
➔ comparison with IR observations of Cas A➔ constraint to gas density in the ambient medium2-1. Dust formation calculation○ Type IIb SN model(SN1993J-like model)－ Meje = 2.94 Msun
MH-env = 0.08 Msun
Mstar = 18 Msun

－ E51 = 1－ M(56Ni) = 0.07 Msun

○ Dust formation calculation－ non-steady nucleation andgrain growth theory(Nozawa et al. 2003)－ onion-like composition

2-2. Composition and mass of dust formed
Mass of dust formed

Total mass of dust :0.167 Msun in SN IIb
0.1-2 Msun in SN IIP

condensation time・ various kinds of dust cancondense in each layer

・ condensation time:300-700 days

2-3. Radius of dust formed in the ejecta
average radius

SN IIbGrain radius➔ > 0.01 μm for SN IIP➔ < 0.01 μm for SN IIb
Dust grains formed in Hdeficient SNe are small

SN IIp (Mstar=20 Msun)

3-1. Calculation of dust evolution in SNRs
○ Model of calculations(Nozawa et al. 2006, 2007)

・ejecta model－ hydrodynamic model fordust formation calculation
・ISM－ Tgas=104 K－ ρ(r) = M/(4 π r2 vw) g/cm-3(M = 2x10-5 Msun/yr)

・treating dust as a test particle－ erosion by sputtering－ deceleration by gas drag－ collsional heating➔ stochastic heating

1.5 pc2.2 pc(1.7 pc)(2.5 pc)

3-2. Evolution of dust in Cas A SNR・ Most of newly formed dust
are destroyed in the hot gas
bacause their radii are small

4-1. Time evolution of IR SEDs for Cas A SNR
240 yr

340 yr

440 yr

540 yr

Data: Hines et al. (2004)
red: with SH
green: without SH4-2. Dependence of IR SED on ambient density
ρ x 1.6

ρ x 3.3

Md = 0.06 Msun

ρx5

ρ x 10Data: Hines et al. (2004)
red: with SH
green: without SH4-3. Contribution from circumstellar dust
・ dust species
C and Mg2SiO4・ dust size distributionf(a)∝a^-3.5
amin=0.001 μm
amax=0.5μm
・ MC : Msil = 3 : 7CMg2SiO4

red: ejecta dust
blue: CSM dust

Summary1) The radius of dust formed in the ejecta of Type IIb SN isrelatively small (＜0.01 μm) because of low ejecta density2) Small dust grains formed in Type IIb SN cannot survive
destruction by the reverse shock3) Model of dust destruction and heating in Type IIb SNR
to reproduce the observed SED of Cas A isMd,eje = 0.06 Msun, Md,ism = 0.03-0.07 Msun
dM/dt = 6.6x10-5 Msun/yr➔ ejecta-dust in denser clump4) IR SED reflects the destruction and stochastic heating➔ density structure of circumstellar medium