The origin of the most iron - poor star Stefania Marassi in collaboration with G. Chiaki, R. Schneider, M. Limongi, K. Omukai, T. Nozawa, A. Chieffi, N.

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

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

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

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

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

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

faint Pop III SN Progenitor of SMSS J031300

Identify the SN progenitor from the observed elemental abundances Limongi & Chieffi 2012

Marassi et al. 2014

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

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

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

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%

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

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

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

work in progress…a complete database of dust from Pop III SNe

Pop III ordinary core-collapse dust grid

faint Pop III calibrated on 4 iron-poor stars

AC [310-3 – 0.3]M

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