2015/12/10

Physical Conditions of Supernova Ejecta Probedwith the Sizes of Presolar Al2O3 Grains- 超新星起源プレソーラーAl2O3粒子の形成環境 (Nozawa, Wakita, Hasegawa, Kozasa, 2015, ApJ, 811, L39)

野沢 貴也（Takaya Nozawa）
国立天文台 理論研究部(National Astronomical Observatory of Japan)

1-1. Summary of observed dust mass in CCSNe

missing cold dust?

young SNRs

Matsuura+2011

Type II-P SNeBalow+2010

Gomez+2012

swept-up IS dust?

There are increasing pieces of evidence that massive
dust in excess of 0.1 Msun is formed in the ejecta of SNe

1-2. Formation and processing of dust in SNe
Nozawa 2014, Astronomical Herald

Destruction efficiency of dust grains by sputtering in thereverse shocks depends on their initial size
The size of newly formed dust is determined by physicalcondition (gas density and temperature) of SN ejecta

1-3. Presolar grains○ Presolar grains‐ discovered in meteorites‐ showing peculiar isotopic compositions

graphite (© Amari)(highly different from the solar system’s materials)‐ thought to have originated in stars before theSun was formed➜ offering key information on nuclear
processes in the parent starsSiC (Nittler 2003)

red giants, AGB stars, supernovae, novae …
‐ mineral composition
graphite, nanodiamond, TiC, SiC, Si3N4,Al2O3, MgAl2O4, TiO2, Mg2SiO4, MgSiO3 …
Al2O3 (Nittler+1997)

1-4. Isotopic composition of presolar oxides○ Oxygen isotopic composition of presolar oxide grainspresolar Al2O3 grains

Group 2
AGB stars

Choi+1998

Group 1RGs

Group 3 / 4
unspecifiedor SNe?

SNeA few particles
of presolar Al2O3
Clayton & Nittler 2004
grains with radii > 0.25 µm
are believed to have been produced in the ejecta of SNe

1-5. Why we focus on presolar Al2O3 grains?
○ Evidence for Al2O3 formation in SNe‐ Infrared spectra of Cassiopeia A (Cas A) SNR➜ Al2O3 is one of the main grain species(Douvion et al. 2001; Rho et al. 2008)〇 Dust formation calculations‐ the first condensate among oxide➜ sizes of Al2O3 grains : < ~0.03 µm

Douvion+2001(e.g., Nozawa+2003; Todini & Ferrara+2001)

Nozawa+2003

destructionin SNRs

Nozawa+2007

1-6. Why the calculated size of Al2O3 is small?
○ One-dimension (1-D) SN models‐ relatively smooth density profile➜ low number density of Al atoms

Nozawa+2003‐ SN ejecta must be inhomogeneous➜ dust formation would proceed ingases with a variety of densities

1-7. Aim of this talk

〇 Question
What is the formation condition of sub-µm-sizedpresolar Al2O3 grains identified as the SN-origin?

〇 Aim
We investigate the condensation of Al2O3 grains
for wide ranges of gas density and cooling rate.

2-1. Supersaturation ratio〇 Supersaturation ratio, S➔ ratio of partial pressure P1 to equilibrium partial pressure P01
gaseous atomc1
For condensation of dust,
S = P1 / P01 > 1➔ lnS = ln(P1 / P01) > 0P01

P1solid (bulk) material
Tdust is assumed
to equal to T=TgaslnS is higher for lower T and higher c1

2-2. Concept of nucleation theoryc1c(2)J2c(3)

J3

αn-1c1cn-1 c(n)Jnβncn・ master equations

2-3. Dust formation calculations (Nozawa & Kozasa 2013)〇 Master equations of cluster formationn＊= 100whereμ = 4πa02σ / kT
σ : surface tension〇 Equation of grain growth
growth rate isindependent ofgrain radius

2-4. Model of calculations for Al2O3 formation〇 Time evolution of gas density (free expansion)
t_0 : the time at which lnS = 0 (S = 1)
c_0 : number density of Al atom at t_0〇 Time evolution of gas temperature
T_0 : gas temperature at t_0
γ: adiabatic constantParameters:- c_{Al,0} = 103-1011 cm-3 (initial number density of Al atoms)- γ = 1.1-1.7 (cooling rate)- t_0 = 300 day (fixed)## condensation efficiency, fcon :## a fraction of Al atoms that are locked up in dust grains

3-1. Size distribution of newly formed grains‐ Size distribution of newly formed grains is lognormal-like with anarrower width for a higher gas density‐ Average grain radius increases with increasing c_{Al,0}➜ a higher gas density leads to more efficient growth of grainsc_{Al,0} should be higher than ~5x108 cm-3 for the formation ofAl2O3 grains with radii larger than ~0.25 µm (diameter of 0.5 µm)

3-2. Scaling relation for fcon,∞ and aave,∞Λon = τsat/τcoll : ratio of supersaturation timescale to gas
collision timescale at the onset time (ton) of dust formation

Λon = τsat/τcoll ∝ τcool ngas
・ fcon,∞ and aave,∞ are uniquely determined by Λon## this is true for the formation of carbon and silicate grains

3-3. Formation condition of presolar Al2O3

normal SNe
1-D model

Λon > 30,000 required➜ at least 10 times higher gas
density than those predictedby 1-D SN models

Submicron-sized presolar Al2O3 grains identified asSN-origin were formed in dense clumps in the ejecta

3-4. Newly formed grains can survive in SNR?
Model of the calculation:
MSN= (3 + 12) Msun, Eexp=1.8x1051 erg,nISM = 1 cm-3

Evolution of dust in SNRs
depends on the initial radii- aini < 0.01 μm➔ completely destroyed- 0.02 μm < aini < 0.1 μm➔ eroded in dense shell- aini > 0.1 μm➔ injected into the ISM

4. Summary of this talkWe investigate the formation of Al2O3 grains for a varietyof densities and cooling rates of the gas.
1) The average radius and condensation efficiency of
newly formed Al2O3 grains are uniquely described by
the non-dimensional quantity Λon.
2) Presolar Al2O3 grains with radii above 0.25 µm can beformed only in the gas with more than 10 times higher
density than those estimated by 1-D SN models.
➜ indicating the presence of dense clumps in the SN ejecta

3) The measured sizes of presolar grains are powerfulprobes for constraining the physical conditions andstructure in which they formed.