2014/03/14

Dust Formation in Extreme
Astronomical Objects
Takaya Nozawa
Kavli IPMU, Univeristy of Tokyo(➔ moving to the theory group of NAOJ from this April)Contents‐Formulation of non-steady-state nucleation‐Dust formation in very massive Pop III stars‐Dust formation in macronovae (or kilonovae)

1. Formulation of non-steady-state
Nucleation

1-1. Uncertainty in classical nucleation theory
・ Application of classical nucleation theory‐sticking coefficient? ➔ usually s = 1‐surface energy of small clusters? ➔ same as the bulk material‐cluster temperature? ➔ Tclus = Tgas
‐shape of small clusters? ➔ sphere‐cluster-cluster reactions? ➔ no‐steady-state nucleation, which cannot be applied in rarefied
astrophysical environments(e.g., Donn & Nuth 1985, but see also Paquette & Nuth 2011)## molecular formation?
➔ complete formation of CO and SiO molecules

1-2. Concept of nucleation theoryc1c(2)J2c(3)

J3

αn-1c1cn-1 c(n)
Jn

βncn

・ master equations

1-3. Non-steady-state nucleation
・ steady-state nucleation rate: Js➔ assuming Js = J2 = J3 = ・・・ = J∞

where μ = 4πa02σ / kT・ non-steady-state dust formationn＊= 100

1-4. Scaling relation of average grain radius
CMgSiO3

Λon > 30

Λon > 30

TN & Kozasa 2013

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・ steady-state nucleation rate is applicable for Λon > 30

1-5. Scaling relation of average grain radius
CMgSiO3

average radiuscondensationefficiency## Λon = τsat/τcoll ∝ τcool ngas

2. Dust Formation in RSG winds ofVery Massive Population III Stars

2-1. Sources of dust in the early unvierse
・ Origin of massive dust at high redshifts (z > 5)
- core-collapse supernovae (CCSNe) may be promising sourcesof dust grains (e.g., Todini & Ferrara 2001; Nozawa+2003; Dwek+2007)- the contribution from AGB stars is also invoked to explain theobserved dust mass (e.g., Valiante+2009; Dwek & Cherchneff 2011)➔ what stellar mass range can mainly contribute dust
budget in the early universe depends on the stellar IMF
Hirano+2014

・ Typical mass of Pop III stars➔ Pop III stars may be much more
massive than Pop I/II stars- ~40 Msun (Hosokawa+2011; Susa 2013)- >300 Msun (Omukai+2003; Ohkubo+2009)- 10-1000 Msun (Hirano+2014)

2-2. Very massive Population III stars
・ Role of very massive stars (MZAMS > ~250 Msun)- emitting numerous ionizing photons➔ reionization of the universe- finally collapsing into black holes➔ serving as seeds of SMBHs

・ Evolution of massive Pop III stars- non-rotating stars with MZAMS > 250Msun
undergo convective dredge-up of C andO during the RSG phase (Yoon+2012)

Yoon+2012- enriching the surrounding medium
with CNO through the RSG winds➔ serving as formation sites of dust
m500vk00

Dust grains formed in the winds are not
likely to be destroyed by the SN shocks

2-3. Model of Pop III red-supergiant winds
・ RSG model: m500vk00 (Yoon+2012)- MZAMS = 500 Msun (no rotation)- L = 107.2 Lsun, Tstar = 4440 K, Rstar = 6750 Rsun
- AC = 3.11x10-3, AO = 1.75x10-3 ➔ C/O = 1.78, Z = 0.034

・ Model of circumstellar envelope- spherically symmetry, constant wind velocity- density profile:- temperature profile:・ Fiducial values of Mdot and Vw- wind velocity: vw = 20 km/s
- mass-loss rate: Mdot = 0.003 Msun/yr➔ losing 90% (208 Msun) of envelope during 7x104 yr

2-4. Chemical equilibrium calculations
major carbon-bearing gas
species other than CO:- atomic carbon
at T > ~1800K- C2H molecules
at T = 1400-1700 K## Formation of PAHs would not## be expectedchemical reactions considered in this study- parameter fc: a fraction of carbon available for dust formation
 fc = 1 as the fiducial case

2-5. Results of dust formation calculations
behavior of dust formation

final size distribution of dust

thick: Model A
thin: Model B

thick: Model A
thin: Model B- carbon grains form around r = 7.5 Rstar (r = 12 Rstar) for
Model A (Model B)- final condensation efficiency is unity for both of the models- final average radius is similar in both Model A and Model B the results are almost independent of chemical reactions

2-6. Dependence on Mdot and vw∝ Mdot0.88

solid: Model A
dashed Model B∝ vw-1.75- The condensation efficiency of dust is unity for the condition;- for the fiducial case (Mdot = 3x10-3 Msun/yr, vw=20 km/s, fc=1)
 1.7 Msun of C grains is produced over the lifetime of the RSG

2-7. How efficient is dust formation?
・ Dust ejection efficiency by very massive Pop III RSGs
- XVMS = Mdust / MZAMS < 3.4x10-3- Mdust / Mmetal < 0.24

・ Dust ejection efficiency by CCSNe (PISNe)- XCCSN = (0.1-30)x10-3 (XPISN < 0.05)- Mdust / Mmetal = 0.01-0.25 (Mdust / Mmetal < 0.15)

Hirano+2014## The ranges above reflects the destruction## efficiency of dust by the reverse shock
CCSNe

If NVMS ~ NCCSN in the Pop III IMF …
➔ The contribution of dust from very
massive RSGs is comparable with,or even higher than that from CCSNe(XVMS NVMS) / (XCCSN NCCSN) > ~1VMS2-8. Expected extinction curves
SMCextinction curves for high-z QSOs

MWGallerani+2010- Extinction curves derived in this study do not resemble any of
the known extinction law such as those in the MW and SMC- The extinction curves observed for high-z quasars do not show
a bump structure, being inconsistent with those given here
➔ The derived extinction curves can be powerful tools to probe
the formation of C grains in very massive Pop III stars

2-9. Composition of low-mass UMP stars- The ultra-metal-poor (UMP) stars with [Fe/H] < -4 would record
chemical imprints of Population III stars- The formation of such low-mass metal-poor stars is triggered
through the cooling of gas by dust produced by Pop III SNe(e.g., Schneider+2012a, 2012b; Chiaki+2014)

・ Possible channel for C-rich UMP star formation- Very massive Pop III RSGs are sources of carbon grains aswell as CNO elements➔ In the gas clouds enriched by Pop III RSGs, carbon grains
enable the formation of low-mass stars whose chemicalcompositions are highly enriched with CNO- We do not predict the presence of heavier elements (Mg, Si, Fe)➔ Further observations and more quantitative theoreticalstudies are needed to show whether any UMP stars haveformed through our scenario2-10. Summary
We have examined the possibility of dust formation in a carbon-richmass-loss wind of a Pop III RSG with M ZAMS = 500 Msun

- For a steady stellar wind, C grains can form with a lognormal-likesize distribution whose average radius is sensitive to wind velocity- The condensation efficiency is unity for➔ the first dust grains in the universe ??
- The mass of C grains is <1.7 Msun （Mdust/MZAMS < 3.4x10-3), which
would be high enough to have impacts on dust enrichment history
in the early universe, if the IMF of Pop III stars were top-heavy# The extinction curves expected from ejected C grains are different fromany known ones
# The chemical feedback by PopIII VMSs predicts a new type of UMP stars

3. Dust Formation in Macronovae

3-1. Sources of r-process elements
・ What are sources of r-process elements?
➔ r-process elements (N > 56) must be
created in neutron-rich environments‐core-collapse supernovae and/or
proto-neutron star wind(e.g., Wanajo+2011; Wanajo 2013)

from Wanajo’s website‐mergers of neutron stars (NS)-NS and/or NS-BH binary(e.g., Korobkin et al. 2012; Bauswein et al. 2013)- ejecta mass:
Mej=0.01-0.1 Msun
- ejecta velocity:
β=v/c=0.1-0.3
Hotokezaka+2013

3-2. Emission from NS-NS/NS-BH mergers
・ Compact star mergers: promising sources of GWs‐position determination with GWs are very uncertain➔ it is needed to probe emission at other wavelengths‐ r-process elements, especially lanthanoids, give high opacityin optical: κ~10 cm2/g compared to κ~0.1 cm2/g in SNe➔ emission from radioactive nuclei
is emitted at infrared wavelengths

・ Macronovae (or called kilonovae)➔ electromagnetic emission involved
in NS-NS and/or NS-BH mergers(energy inputs may be due to decayof radioactive r-process elements)## ref. Energy inputs of other eruptive objects- novae: explosive nucleosynthesis on the surface- supernovae: decay of 56Ni produced at explosion

Tanaka & Hotokezaka+2013

3-3. Macronovae: GRB 130603B
Short GRB 130603B (z = 0.356)

afterglow

NIR excess

Gamma-ray bursts (GRBs)- Short GRBs (<~2 sec):
originating from mergers ofcompact objects- Long GRBs (~2-10 sec):
originating from collapses ofmassive stars(accompnied with SNe Ib/Ic)

excess of NIR around 7 day‐processing of optical light byr-process elements
Tanvir+2014, Nature‐NS-NS (NS-BH) merger is theformation sites of r-processelements

3-4. Dust formation in Macronovae
・Dust formation calculations

condensation efficiency‐gas density‐gas temperature
T0=2000K, s=0.8‐r-process elements cannot
condense into dust grains‐formation of C (and Fe)
grains could be possible

Takami, TN, Ioka 2014 in prep

3-5. Dust in Macronovae
thermal emission from C grains‐NIR detection of GRB 130603B
around 7 day can be explainedby thermal emission from hot(~1800 K) C grains with themass of ~10-5 Msun
Takami, TN, Ioka 2014 in prep

condensation efficiency of C grains

amount of C atom to achieve
10-5 Msun of C grains‐NS-NS merger (ΔΩ/4π~1)➔ MC = 4x10-3 Msun
‐NS-BH merger (ΔΩ/4π~0.1)➔ MC = 4x10-4 Msun

3-6. Summary
We have examined the possibility of dust formation in the ejecta ofmacronovae based on observed properties of GRB 130603B‐ In the high-density case with efficient r-process nucleosynthesis,
r-process elements never condense into dust grains even if they
are abundantly produced‐ In the low-density case with inefficient r-process nucleosynthesis,
carbon grains can form with quite small radius (<0.02 μm)‐ The near-infrared excess observed for GRB 130603B is explainedby thermal emission of carbon dust formed in the ejecta# sources of cosmic dust :- SNe (Type II SNe and Type Ia SNe),- mass-loss winds of evolved stars (AGB, RSG and WR stars)- mass-loss winds of massive main-sequence stars➔ Extreme astronomical objects are good laboratories for examining
the process of dust formation (testing the theory of dust formation)