2012/11/01

Formation of Dust in the Ejecta
of Type Ia Supernovae
Takaya Nozawa
IPMU (Institute for the Physics and Mathematicsof the Universe, University of Tokyo)

Collaborators:
K. Maeda (K-IPMU), T. Kozasa (Hokkaido University)
M. Tanaka, (NAOJ), K. Nomoto (K-IPMU),
H. Umeda (Univ. of Tokyo)
Nozawa et al. 2011, ApJ, 736, 45

1-1. Introduction〇 Type Ia supernovae (SNe Ia)－ thermonuclear explosions of C+O white dwarfs withthe mass close to Chandrasekhar limit (~1.4 Msun)・ deflagration (Nomoto+76, 84)➔ subsonic wave, unburned C in the outer layer・ (delayed) detonation (Khokhlov91a, 91b)
➔ supersonic wave, burning almost all C－ synthesize a significant amount of Fe-peak andintermediate-mass elements such as Si, Mg, and Ca➔ play a critical role in the chemical evolution➔ possible sources of interstellar dust?

1-2. Type Ia SNe are sources of dust?
〇 Suggestions on dust formation in SNe Ia－ SNe Ia may be producers of Fe grains(Tielens98; Dwek98)－ the isotopic signature of presolar type X SiC grains
can be explained if produced in SNe Ia (Clayton+97)〇 Observations of normal SNe Ia－ no increase of IR dust continuum (and no CO emission)－ no rapid decrease of the optical light curve－ no blueshift of atomic line emissions➔ these signatures have been reported for CCSNe－ no evidence for ejecta-dust in Tycho SNR (Douvion+01)

1-3. Aim of our study〇 Questions－ Are there any differences in formation process ofdust between SNe Ia and (Type II) CCSNe?

－ Is it possible for dust grains to form in SNe Ia ?

〇 Dust formation calculation in SNe Ia➔ chemical composition, size, and mass of dust thatcan condense in the ejecta of SNe Ia➔ dependence of dust formation process on SN types➔ implication on the outermost layer in SNe Ia➔ survival of the newly formed grains against
destruction by the reverse shock2-1. Model of SNe Ia (1)〇 Type Ia SN model

elemental composition

C-deflagration W7 model(Nomoto+84; Thielemann+86)－ Meje = 1.38 Msun
－ Ekin = 1.3x1051 erg－ M(56Ni) = 0.6 Msun## M(56Ni) ~ 0.06 Msun intypical CCSNe－ stratified distribution(no mixing of elements)## This assumption issupported observationally(e.g. Mazzali+08; Tanaka+11)

0.1 Msun of C + O
remained unburnedin the outermost layer
with MC/MO ~ 1

2-2. Model of SNe Ia (2)hydrodynamic model

red lines : SNe Ia
・ Meje = 1.38 Msun
・ Ekin = 1.3x1051 erg
blue lines : Type II-P SNe・ Mstar = 20 Msun
・ Ekin = 1.0x1051 erg
・ Menv = 13.2 Msun

－ gas density in the SN Ia
is more than 3 orders ofmagnitude lower thanthat in the SN II-P－ gas temperature in theSN Ia decreases morequickly2-3. Calculation of dust formation〇 nucleation and grain growth theory(Nozawa+03, 08, 10)－ steady-state nucleation rate2

－ grain growth rate

－ sticking probability : α = 1 and 0.1－ LTE condition : Tdust = Tgas
(dust has the same temperature as the gas)

The use of the same prescription enables the directcomparison with our earlier results

3-1. Results (1): Condensation time of dust
Condensation time

Condensation temperature－ different dust species
form in different layers・ Fe and Ni grains cannot
condense significantly
・ SiC can never condense－ condensation time of dust
: tc = 100-300 days
(tc > ~300 days in SNe II-P)3-2. Results (2): Average radius of dust
SN Ia

SN II-P

0.01 μm
0.01 μm

SN IIbaverage radius of dust
0.01 μm: aave < ~0.01 μm➔ because of low densityof gas in the expanding
ejectathe radius of dust formedin H-stripped SNe is small

・ SNe IIb/Ia with thin/noH-env ➔ aave < 0.01 μm
・ SN II-P with massive
H-env ➔ aave > 0.01 μm

3-3. Results (3): Mass of each dust species
α=1α = 0.1

MC= 0.006 Msun

Msilicate = 0.030 Msun
MFeSMSi= 0.018 Msun
= 0.063 Msun

Mtotal

= 0.116 Msun

Total mass of dust formed in SNe Ia : Mdust < ~0.1 Msun

4-1. Optical depths by newly formed dust
V band (0.55 μm) opacity at 300 days for α = 1
MC= 0.006 Msun
Msilicate = 0.030 Msun
MFeS = 0.018 Msun
MSi= 0.063 Msun

τC= 22τsilicate = 0.01
τFeS = 14
τSi= 78Mtotalτtotal= 0.116 Msun

= 114

V band (0.55 μm) opacity at 300 days for α = 0.1
Mtotal~ 3x10-4 Msun

τtotal=1Formation of dust grains (C, Si, and Fe) should be
suppressed to be consistent with the observations

4-2. Non-LTE effect on dust formation

Non-LTE dust formation
MFeS = 4x10-4 Msun
Msi = 1x10-6 Msun
➔ τFeS < 0.1 after 300 day

MC = 0.0055 Msun
➔ τC > 20 (too high to be consistent with the observations)4-3. Infrared thermal emission from dust
Observational data : SN 2005bf
at day 200 and 400 (Gerardy+07)

black solid lines :SEDs including
emission from C grains➔ much higher than theobservational results

red solid lines :SEDs not including
emission from C grains➔ not contradict with theobservational results
0.03 Msun of silicate canbe allowed as dust mass

4-4. Carbon dust and outermost layer of SNe Ia〇 Formation of massive carbon dust
－ high sticking probability of α = 0.1-1➔ if α < ~0.01, any dust grain cannot condense－ dust formation around 100 days, M(56Ni) ~ 0.6 Msun
➔ dust formation can be destroyed by energetic
photons and electrons prevailing in the ejecta－ massive unburned carbon (~0.05 Msun) in deflagration➔ change of WD composition by the He-shell flash➔ burning of carbon by a delayed detonation wave

observationally estimated carbon mass in SNe Ia :Mc < 0.01 Msun (Marion+06; Tanaka+08)

4-5. Dust formation in super-Chandra SNe?
－ super-Chandra SNe :M(56Ni) ~ 1.0 Msun

SN 2009dc, Tarbenberger+’10

detection of CII line
➔ presence of massive
unburned carbon
SN 2006gz, Maeda+09

enhanced fading at ~200 day➔ formation of carbon dust?

5-1. Destruction of dust in Type Ia SNRs
－ 10-3 Msun of dust cansurvive for nH ~ 0.01 cm-3
but too low ISM density－ typical ISM gas density
around SNe Ia➔ nH = 1-5 cm-3
(Borkowski+06)

newly formed grains arecompletely destroyed for
ISM density of nH > 0.1 cm-3

SNe Ia are unlikely to be major sources of dust

Summary－ For α = 1, C, silicate, Si, and FeS grains can condense in the ejectaof SNe Ia at 100-300 days, being earlier than >300 days in SNe II-P.
－ Due to the low gas density in the ejecta, the average radii of dust
grains are below 0.01 μm, being smaller than those in SNe II-P.
－ The total mass of dust that can form in the ejecta of SNe Ia is up to
0.1 Msun. (0.03 Msun of silicate is more conservative.)－ Formation of C grains is inconsistent with the observations➔ low sticking probabilities of α < ~0.01➔ small C clusters can be destroyed by photons and electrons➔ preexisting C should be almost completely burned－ For the ISM density of nH,0 > 0.1 cm-3, the newly formed grains arealmost completely destroyed before being injected into the ISM.
➔ SNe Ia are likely to be poor producers of interstellar dust