s-process in c-rich emps: predictions versus observations sara bisterzo (1) roberto gallino (1)...

S-Process in C-Rich EMPS: S-Process in C-Rich EMPS: predictions versus predictions versus

observationsobservationsSara Bisterzo Sara Bisterzo (1)(1)

Roberto Gallino Roberto Gallino (1)(1)

Oscar Straniero Oscar Straniero (2)(2)

I. I. Ivans I. I. Ivans (3, 4)(3, 4)

andandWako Aoki, Sean Ryan, Timoty C. BeersWako Aoki, Sean Ryan, Timoty C. Beers

(1)(1) Dipartimento di Fisica Generale , Università di Torino, Dipartimento di Fisica Generale , Università di Torino, 10125 (To) Italy10125 (To) Italy

(2) (2) Osservatorio Astronomico di Collurania – Teramo, 64100Osservatorio Astronomico di Collurania – Teramo, 64100 (3)(3)The Observatories of the Carnegie Institution of The Observatories of the Carnegie Institution of

Washington, Pasadena, CA, (USA) Washington, Pasadena, CA, (USA) (4)(4)Princeton University Observatory, Princeton, NJ (USA)Princeton University Observatory, Princeton, NJ (USA)

TP

Convective envelope

He-intershell

22Ne(a,n)25Mg

During the TDU (third dredge-up) p ingestion in the top of He-intershell (few protons).

At H-shell ignition 13C-pocket formation via 12C + p 13N + , and 13N()13CAt T~ 108 K 13C(a,n)16O in

radiative conditions s-process.

13C(a,n)16O

Neutron source: 12C(p,)13N(+)13C(,n).

Type: primary

When: interpulse T6>90.

Where: He-intershell

Density: 106-107 (n/cm3)

Straniero et al. 1995, Gallino et al. 1998

The AGB engine

The two neutron sources in AGB stars

13C(,n)16O 22Ne(,n)25Mg

Needs 13CMajor neutron source13C-pocketPrimary source!T8 = 0.9-1Interpulse phase(1- 0.4) 105 yrRadiative conditionsNn = 107 cm-3

Abundant 22Ne Minor neutron sourceNeutron burstSecondary (primary) sourceT8 = 3 (low 22Ne efficiency)Thermal pulse6 yrConvective conditionsNn (peak) = 1010 cm-3

AGB models at AGB models at very low [Fe/H]very low [Fe/H]

M = 1.5 Msun

1.2 Msun < M < 3 Msun

13C-pocket: ST*2 …. ST/100 Constant pulse by pulse(ST: 4.10-6 Msun , [Fe//] = -0.3, Reproduction of Solar Main Component )

1.2 Msun 3 pulses 1.3 Msun 6 pulses1.4 Msun 8 pulses1.5 Msun 20 pulses2 Msun 26 pulses3 Msun 30 pulses

Mass loss : from 10-7 to 10-4 Msun/yr Reimers

1.2 Msun η = 0.3 1.3 Msun η = 0.31.4 Msun η = 0.31.5 Msun η = 0.32 Msun η = 0.53 Msun η = 1

At very low metallicityAt very low metallicity

Today, Intrinsic AGB halo stars:

typical mass is ~ 0.6 Msun (initial mass 0.8 – 0.9 Msun)

NO TDU No C or s-process enrichment

observable.

Then all CRUMPS are Extrinsic AGB Then all CRUMPS are Extrinsic AGB starsstars::

Binary systems transfer of material C- and s-rich on the companion (through stellar wind, Roche Lobe …).

The unevolved companion shows the tipical AGB composition, while the true AGB star is now a White Dwarf.

Extrinsic AGB modelsExtrinsic AGB models

transf

ini

M

envMdil

)(log

Diluition factor: used to simulate the mixing effect in the envelope of the extrinsic stars

)(

)(log

tranfM

obsMdil

AGB

star

)(

)(log

transfM

obsMdil

AGB

star

Note: for main sequence stars dil ≈ 0 for giants dil may be important

AGB models: envelope abundancesAGB models: envelope abundances

ls

hsPb

M ≈ 1.5 Msun

To reproduce stars with both s+r enhancementsTo reproduce stars with both s+r enhancements

Different choice of initial chemical abundances of Eu in the progenitor clouds [Eu/Fe]ini from 0.5 to 1.5 and 2.0

Effect of pre r-enrichment in s-enhanced stars

Model with pre r-enrichment normalized to [Eu/Fe]ini = 2.0 in the parental cloud: the envelope abundances in these stars are predicted by mass transfer from the more massive AGB companion in a binary system which formed from a parental cloud already enriched in r elements.

r-process rich

AGB star model of M ≈ 1.3 Msun with [Fe/H] = - 2.60.

NO r-process rich

[Eu/Fe]ini = 2.0[Eu/Fe]ini = 0.0

Choice of initial abundances

The choice of the initial r-rich isotope abundances normalised to Eu is made considering the r-process solar prediction from Arlandini et al.1999.

1- Lead stars (C, s, Pb rich)1- Lead stars (C, s, Pb rich)2 – C and 2 – C and s+r richs+r rich Lead stars Lead stars

References1. J. A. Johnson, M. Bolte, ApJ 579, L87 (2002)2. W. Aoki, et al., ApJ 580, 1149 (2002)3. T. Sivarani, et al., A&A 413, 1073 (2004)4. J. A. Johnson, M. Bolte, ApJ 605, 462 (2004)5. W. Aoki, et al., ApJ 561, 346 (2001)6. S. Van Eck, S. Goriely, A. Jorissen, B. Plez, A&A 404, 291 (2003)7. S. Lucatello, et al., AJ 125, 875 (2003)

1.8*

8. J. G. Cohen, N. Christlieb, Y. Z. Quian, G. J. Wasserburg, ApJ 588, 1082 (2003)9. B. Barbuy, et al., A&A 429, 1031 (2005)11. I. Ivans et al., ApJ accepted (2005)

•[Eu/Fe] measured; **sigma(dil) = ± 0.2 dex

NOTE: Initial Mass are estimates dependent also on mass loss rates adopted

Teff = 5850 K

Teff = 6625 K

2 – C and s+r rich Lead stars2 – C and s+r rich Lead stars

0.0

Without r-process enhancement [Eu/Fe] ini = 0.0

With r-process enhancement [Eu/Fe] ini = 2.0

HE2148-1247 Cohen et al. 2003

Teff = 6380 K

Prediction updated

Extrinsic AGBs indicator

CS29497-030 Ivans et al. 2005



Teff = 7000 K

The s elements enhancement in low-metallicity stars interpreted by mass transfer in binary systems (extrinsic AGBs). For extrinsic AGBs [Zr/Nb] ~ 0. Instead, for intrinsic AGBs [Zr/Nb] ~ – 1.

Zr over Nb: Intrinsic or Extrinsic AGBs

M ≈ 1.3 Msun

[Fe/H] = -2.60

Fig. 2s-process path

Case ST*2[Eu/Fe]ini = 2.0



CS29497-34 Barbuy et al. 2005

Teff = 4800 K



CS31062-050 Aoki et al. 2002

Teff = 5600 K


Teff = 5500 K

Barklem et al. 2005: s-enhanced starsBarklem et al. 2005: s-enhanced stars

Star [Fe/H] [C/Fe] [Mg/Fe] [Sr/Fe] [Y/Fe] [Zr/Fe] [Ba/Fe] [La/Fe] [Ce/Fe] [Nd/Fe] [Sm/Fe] [Eu/Fe]

CS 22892-052 -2.95 1.00 0.12 0.61 0.45 - 1.19 1.02 - 1.14 - 1.54

HE 0131-3953 -2.71 2.45 0.30 0.46 - - 2.20 1.94 1.93 1.76 - 1.62

HE 0202-2204 -1.98 1.16 -0.01 0.57 0.41 0.47 1.41 1.36 1.30 1.02 1.03 0.49

HE 0231-4016 -2.08 1.36 0.22 0.67 0.72 - 1.47 1.22 1.53 1.35 - -

HE 0338-3945 -2.41 2.07 0.39 0.73 0.73 - 2.41 2.26 2.21 2.09 - 1.89

HE 0432-0923 -3.19 0.24 0.34 0.47 0.51 0.88 0.72 - - - - 1.25

HE 1105+0027 -2.42 2.00 0.47 0.73 0.75 - 2.45 2.10 - 2.06 - 1.81

HE 1127-1143 -2.73 0.54 0.22 0.24 0.22 - 0.63 - - 0.86 - 1.08

HE 1135+0139 -2.33 1.19 0.33 0.66 0.36 0.46 1.13 0.93 1.17 0.77 - 0.33

HE 1343-0640 -1.90 0.77 0.37 0.68 0.51 0.98 0.70 - - - - -

HE 1430-1123 -2.71 1.84 0.35 0.24 0.50 - 1.82 - - 1.72 - -

HE 2150-0825 -1.98 1.35 0.36 0.66 0.85 0.97 1.70 1.41 1.48 1.42 - -

HE 2227-4044 -2.32 1.67 0.30 0.41 - - 1.38 1.28 - - - -

HE 2240-0412 -2.20 1.35 0.28 0.24 - - 1.37 - - - - -

CONCLUSIONS:CONCLUSIONS:The spectroscopic abundances of low-The spectroscopic abundances of low-

metallicity s- and r-process enriched stars metallicity s- and r-process enriched stars are interpreted using theoretical AGB are interpreted using theoretical AGB models (FRANEC CODE),models (FRANEC CODE), with an initial with an initial composition already enriched in r elements composition already enriched in r elements from the parental cloud from which the from the parental cloud from which the binary system was formed.binary system was formed.

[Zr/Nb] is an indicator of an extrinsic AGB in [Zr/Nb] is an indicator of an extrinsic AGB in a binary system: [Zr/Nb] ~ 0 for an extrinsic a binary system: [Zr/Nb] ~ 0 for an extrinsic AGB, [Zr/Nb] ~ AGB, [Zr/Nb] ~ –– 1 for an intrinsic AGB. 1 for an intrinsic AGB.

Spectroscopic determination of [Na/Fe] and Spectroscopic determination of [Na/Fe] and [Mg/Fe] permits an estimate of the initial [Mg/Fe] permits an estimate of the initial AGB stellar mass.AGB stellar mass.

CONCLUSIONS:CONCLUSIONS: Open ProblemOpen Problem: the strong discrepancy of C : the strong discrepancy of C

and N predictions with respect to and N predictions with respect to observations may be reconciled:observations may be reconciled:

(1)(1) by introducing the effect of cool bottom by introducing the effect of cool bottom process (CBP) in the TP-AGB phase (*);process (CBP) in the TP-AGB phase (*);

(2)(2) for N and [Fe/H] < -2.3, by the effect of for N and [Fe/H] < -2.3, by the effect of Huge First TDU (see Gallino presentation).Huge First TDU (see Gallino presentation).

(3)(3) Uncertainties in the spectroscopic Uncertainties in the spectroscopic abundances of C, N, O, Na, Mg abundances of C, N, O, Na, Mg M. M. Asplund, ARAA 2005Asplund, ARAA 2005

(*) Nollett, K. M., Busso, M., Wasserburg, G. J., ApJ 582, 1036 (2003);Wasserburg, G. J., Busso, M., Gallino, R., Nollett, K. M., (2006), Nucl. Physics, in press.

s-process in c-rich emps: predictions versus observations sara bisterzo (1) roberto gallino (1)...

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