the origin of the most iron - poor star stefania marassi in collaboration with g. chiaki, r....
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The origin of the most iron-poor star
Stefania Marassiin collaboration with
G. Chiaki, R. Schneider, M. Limongi, K. Omukai,
T. Nozawa, A. Chieffi, N. Yoshida
David Meeting Pisa 13-15 october 2014
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carbon-enhanced metal poor stars
CEMP – r/s: mass transfer from an AGB companion in binary systems
CEMP – no: metal yields from faint Pop III SNe with mixing/fallback
~ 20 % of stars with [Fe/H] < -2 are C-enhanced: [C/Fe] > 0.7
Yong et al. 2013; Norris et al. 2013
[C/Fe] > 0.7
C-normal: metal yields from
ordinary Pop III core-collapse SNe
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the most iron-poor stars in the Galactic halo
HE 0107-5240[Fe/H] = -5.4
Christlieb et al 02,04,08
HE 1327-2326[Fe/H] = -5.7
Frebel et al 05
HE 0557-4840[Fe/H] = -4.75
SDSS J102915+172927[Fe/H] = -4.99
Caffau et al 11
Z ≈ 7 10-3 Zsun Z ≈ 2 10-2 Zsun Z ≈ 10-3 ZsunZ < 5 10-5 Zsun
Norris et al. (2008)
CEMP: C-enhanced metal poor stars C-normal
SMSS J031300.36-670839.3[Fe/H] < -7.1
Keller et al 14
Z≈2.67 10-3 Zsun
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C-normal and C-rich stars: different formation pathways?
stars with [Fe/H] < -3.5 can not form through metal line-cooling
The different composition in the material out of which these low-mass stars form suggest that their formation relies on two different cooling channels: fine-structure-line cooling and dust cooling
Ji et al.2013
Dtrans = Log(10[C/H] + 0.9 10[O/H])
Schneider et al. 2012dust formed in 20-35 M Pop III SN ejecta is enough to activate Dust-driven fragmentation if the D > Dcr = (4.4 ± 2.0) x 10-9
Both dust-cooling and fine structure cooling are relevant for low mass star formationand there is a tentative evidence that fine structure cooling and dust-cooling are mutually exclusive
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A single low-energy, iron-poor SN as the source of metals in SMSS
J031300 Keller et
al.2014
[Fe/H]<-7.1 is 30 times lower than the iron abundance in HE1327-2326 (Frebel star)
It is the first time that the abundance patterns could be interpreted requiring a single SN event
Best fit of the observed abundances in Keller et al.2014
SN explosion of a 60M progenitor with E=1.8×1051erg with extensive fallback Faint SN
[Fe/H]<-7.1 Z≈2.67 Z
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Faint SN progenitor
Mixing and fallback model during the SN explosion internal mixing occurs up to a small region outside the mass cut
a small amount of the mixed material is expelled from the star with most of it falling back into the central regionUmeda & Nomoto 2002/2003
Tominaga et al. 2007
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faint Pop III SN Progenitor of SMSS J031300
Identify the SN progenitor from the observed elemental abundances Limongi & Chieffi 2012
Marassi et al. 2014
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Dust formation model: classical nucleation theory
Todini &Ferrara (2001), Schneider, Ferrara,Salvaterra (2004), Bianchi & Schneider ( 2007)
The formation of solid particles in a gaseous medium happens when a gas becomes supersaturated. It is a two step process:
-the formation of a seed clusters (monomers), that is prevented until the condensation barrier is exceeded
-the growth of this clusters by accretion of other monomers
we follow the formation of different solid compounds:AC (amorphous carbon) Al2O3 (corundum) Fe3O4 (magnetite)
MgSiO3(enstatite) Mg2SiO4 (forsterite) SiO2 (silicon dioxide)
+ CO , SiO, C2, O2 Molecule formation and destruction
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Dust formation model: updated molecular network
we assume that formation/destruction of CO , SiO, C2 and O2 is regulated by radiative association process and bimolecular process
another destruction process of CO and SiO is the impact with theenergetic electrons produced by the radioactive decay of 56Co
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Impact on dust of the ejecta mixing
MCO=2.15 MAC=0.16 80M3DMCO=1.44 MAC =0.27 80M1D
layer A: MCO=1.27 MAC= -layer B: MCO =4.3x10-2 MAC= 0.11
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Impact on dust of the reverse shockmass of dust that survives for increasing
shock strengths
depending on progenitor the fraction of surviving dust is between a few to 80%
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The birth environment of SMSS J031300
One-zone semi-analytic collapse calculation to follow thetemperature evolution of the cloud polluted by a single SN Chiaki et al. 2014
fragmentation due to line cooling
fragmentation due to dust
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prediction vs observations:C-normal and C-rich
C-normal star: enriched by normal Pop III SN with silicate dust
C-rich star: enriched by faint Pop III SN with carbon dust
DTRANS Critical transition discriminant for fine-structure line cooling Frebel et al. 2007
Range of critical [Si/H]cr abundances to activate dust cooling Chiaki et al. 2014
Range of critical [C/H]cr abundances to activate dust cooling Marassi et al.2014
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Critical conditions in terms of the dust-to-gas ratioCritical dust-to-gas-ratio for dust
coolingDcr=[2.6-6.3]x10-9
Schneider et al. 2012
C-normal and C-rich stars populate the region of the plane: the two critical conditions are not mutually exclusive
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work in progress…a complete database of dust from Pop III SNe
Pop III ordinary core-collapse dust grid
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faint Pop III calibrated on 4 iron-poor stars
AC [310-3 – 0.3]M
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summarizing
We estimate metal yields and dust produced in faint Pop III SN explosions fitting the elemental abundances on the surface of SMSS J031300
Faint Pop III SNe produce dust, but contrary to ordinary core-collapse SNe, only AC forms in the ejecta
The amount of dust formed depends on the reverse shock strenght and on mixing efficiency
The formation of SMSS J031300 may have been triggered by dust cooling and fragmentation
C-normal and C-rich stars may have followed a common formation pathway
We are building a complete dust database from Pop III SNe
Thanks for you attention