Formation and evolution of dust in
Type IIb SN: Application to Cas A
Takaya Nozawa(IPMU, Univ. of Tokyo)
Collaborators;
T. Kozasa (Hokkaido Univ.), N. Tominaga (Konan Univ.),
K. Maeda (IPMU), H. Umeda (Univ. of Tokyo),
K. Nomoto (IPMU/Univ. of Tokyo)

1. Introduction

1-1. Background
CCSNe are main sources of interstellar dust?
－ formation of dust in metal-rich ejecta of SNe－ destruction of dust in shocked gas inside SNRs
・ Theoretical studies－ various dust species with 0.001-1 μm
Mform = 0.1-1 Msun for SNe II-P(Todini & Ferrara ’01; Nozawa+’03)－ Msurv = 0.01-0.8 Msun for nH,0=10-0.1 cm-3
(Bianchi & Schneider ’07; Nozawa+’07)➔ 0.1-1 Msun of dust per SN II are required to explain alarge amount of dust (108 -109 Msun ) for QSOs at z > 5(Morgan & Edmunds 2003; Dwek et al. 2007)

1-2. Dust-forming SNe
・ Observations of dust-forming SNe－ few information on composition and size of dust
➔ a limited quantity and quality of observations－ Mdust < 10-3 Msun
➔ assuming the ejecta is optically thin➔ some species of dust grains quickly cool downderived dust mass can be underestimated・ sophisticated radiative transport model

・ UV/optical to far IR observation data

1-3. Nearby, young SNRs
For nearby, young SNRs
・ Comparison of models with IR observations of SNRs

－ erosion by sputtering and stochastic heating－ envelope-poor SNe are more favorable(For Type II-P SNe, the reverse shock collides with the He
core after a few thousand years)－ ~30% of CCSNe explode as SNe Ib/c and SN IIb(Prieto+’09; Smartt+’08; Boissier & Prantzos ’09)

・ Dust formation and evolution in SN with thin envelope－ how formation and destruction processes of dust
depend on the thickness of outer envelope?
－ apply the results to IR observations of Cas A

1-4. Cassiopeia A SNR○ Cas A SNR－ age: ~330 yr (Thorstensen+’01)－ distance: d=3.4 kpc (Reed+’95)－ 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 ’03)

－ oxygen-rich SNR
detection of a lot of metal lines (O, Ar, S, Si, Fe …)
thermal emission from ejecta-dust➔ Mdust = 0.02-0.054 Msun (Rho+’08)－ SN type : Type IIb (Krause+’08)

2. Formation of dust in Type IIb SN

2-1. Calculation of dust formation○ nucleation and grain growth theory (Kozasa & Hasegawa ‘87)
key species: a gas species with the least collision
frequency among reactants
nucleation rate

grain growth rate

・ time evolution of gas density and temperature・ elemental composition of the gas

2-2. Model of Type IIb SN (1)○ SN IIb model (SN1993J-like model)－ Meje = 2.94 Msun
MH-env = 0.08 Msun
Mstar = 18 Msun
－ E51 = 1－ M(56Ni) = 0.07 Msun

○ mixing of elements－ original onion-like composition○ formation of molecules ➔ complete
C/O < 1 ➔ all C atoms are locked into CO
C/O > 1 ➔ all O atoms are locked in to CO
Si/O < 1 ➔ all Si atoms are locked into SiO

2-3. Model of Type IIb SN (2)small ejecta mass of TypeIIb SN↓
very high velocity of gas
in the He core↓
very low gas density inthe He core of Type IIb SN

2-4. Composition and mass of dust formed
condensation time・ different species of dust cancondense in different layers
・ condensation time:300-700 days

mass of dust formed

Total mass of dust formed :0.167 Msun in SN IIb
0.1-1 Msun in SN II-P

2-5. Average radii of dust formed in the ejecta
SN IIbGrain radius➔ > 0.01 μm for SN IIP➔ < 0.01 μm for SN IIb
Dust grains formed in Hdeficient SNe are small

SN II-P

SN Ib (SN 2006jc)

Nozawa et al. (2008)

3. Evolution of dust in Type IIb SNR

3-1. Calculation of dust evolution in SNRs
○ time evolution of gas temperature and density in SNR・ejecta modelhydrodynamic model for dust formation calculation

・CSM gas density－ uniform :nH,0 = 0.1, 1, 10 cm-3
－ stellar wind : nH,1 = 30, 120, 200 cm-3
nH(r) = nH,1 (r / r1)-2 r < r2
= 1 cm-3r ≥ r2
○ time evolution of dust (Nozawa+’06, ’07)
・treating dust as a test particle－ erosion by sputtering and deceleration by gas drag➔ initial size distribution and spatial distribution of dust・calculations are performed up to ~106 yr

3-2. Calculation of dust evolution in SNRs
downward-pointing arrows➔ positions of the forward
and reverse shocks

The temperature of the gas
swept up by the reverse andreverse shocks is 106 -108 K.

Dust grains residing in thishot gas are eroded by
sputtering3-3. Calculation of dust evolution in SNRs
The collision times between
the reverse shock and He coreis 75 year after the explosion➔ much earlier than those(> 1000 yr) for Type II-P

small grains formed in theejecta are quickly trapped inthe hot gas and are completelydestroyed

3-4. Time evolution of dust mass
nH,0=1.0 /cc

nH,0=10 /cc

Mdust ~ 10-4 Msun at 105 yr

Mdust = 0 Msun at 105 yr

higher ambient density leads to the earlier arrival of thereverse shock at the dust-forming region
higher gas density causes more efficient decelerationand destruction of dust

3-5. Time evolution of total dust mass

Almost all newly formed dust grains are destroyed in theshocked gas within the SNR➔ small grain size of newly formed dust
➔ early arrival of the reverse shock at the He core

4. Thermal emission of dust in SNRs

4-1. Thermal emission from dust in the SNR・ thermal radiation from dust ← temperature of dust
・ equilibrium temperature of dust in SNR is determined bycollisional heating with gas and radiative cooling
H (a, n, Tg)= Λ(a, Qabs, Td) ➔ thermal emission
・ small-sized dust grains (＜0.01 μm) ➔ stochastic heating

4-2. Time evolution of IR thermal emission (1)nH,0=1 /cc

Data: Hines et al. (2004)
red: with SH
green: without SH4-2. Time evolution of IR thermal emission (2)nH,0=10 /cc

Data: Hines et al. (2004)
red: with SH
green: without SH4-3. Dependence of IR SED on ambient density

dM/dt = 2x10-5 Msun/yr

Md = 0.008 Msun
dM/dt = 8x10-5 Msun/yr

4-4. Contribution from circumstellar dust
・ dust species
C and silicate
・ dust size distributionf(a) ∝ a^-3.5
amin = 0.001 μm
amax = 0.5 μm
・ dust-gas ratio: parameterC・ thermal emission fromboth CS grains has apeak at λ~30 μm

Silicate

red: ejecta dust
blue: CSM dust

4-5. Contribution from unshocked dustMd,warm ~ 0.008 Msun,Md,cool ~ 0.07 Msun
dM/dt = 8x10-5 Msun/yr・observed SED can bewell reproduced If thetemperature of unshocked
cold dust is around 40 K

Summary1) The radius of dust formed in the ejecta of Type IIb SN isquite small (＜0.01 μm) because of low ejecta density
2) Small dust grains formed in Type IIb SN cannot survive
destruction in the shocked gas within the SNR

3) IR SED reflects the destruction and stochastic heating➔ properties (size and composition) of dust
➔ density structure of circumstellar medium4) Model of dust destruction and heating in Type IIb SNR
can reasonably reproduce the observed SED of Cas A;
Md,warm = 0.008 Msun, Md,cool = 0.07 Msun
dM/dt = ~8x10-5 Msun/yr