AGB stars

Inma Dominguez Sergio CristalloOscar Straniero

Evolution of Low & Intermediate Mass Stars

M 8 M C-O White Dwarfs

MCO ~ 1.1 M C ignition MMS = MUP ~ 8 M

Becker, Iben 1979-80

Hertzsprung-Russell Diagram

H central

burning

He central

burning

TP-AGB

E-AG

B

RGB

Pre

Main Sequence

FDU

AGB stars

12C & 14N Life cycles 7Li (BBN) 26Al (Early SS) s-elements main & strong component (88 A 210)

Thermal pulses 3er Dredge-up Mass Loss

Nucleosynthesis 75% of the mass return to the ISM

HBB Mixing process CBP

Pieces of their envelopes Meteorites

Not an easy phase

Solar System Abundances

Anders & Grevesse 1989Cameron 1982

SNIIBBN

SNII

SNIa

AGB

SNII ?

BBN

WeakA<90

Main90<A<204

Strong204<A<210

Beyond Fe-peak: neutron captures

AGB

AGB

Why to care about AGBs ? Final phase of the evolution of stars with M < 8 M

the Majority !! PNe WDs Novae/Thermonuclear SNe Border: WD or Core Collapse Sne

Initial to Final Mass Relation Mass return to ISM WD Progenitors of Type Ia

75% to the total mass return from to the ISM (Sedlmayr 1994)

Elements Beyond the Fe peak (A > 85) slow neutron captures (s-process)

Why to care about AGBs ?

Contamination of the protosolar nebula right before its collapse by a local source AGB or SN ?? AGB star !!! (Wasserburg et al. 1994,1995, 2006;Busso et al. 1999)

26Al 36Cl 41Ca 60Fe 107Pd (radiactivities)

Most extrasolar grains recovered in meteorites

Pieces of AGB stars in terrestial laboratories !!

C and N, crucial for organic chemistry and life cycles half of all the observed 12C (?) at least 30% !!

7Li (Nucleosynthesis of the Light Elements)

Dredge-ups The bottom of the Convective Envelope (CE) moves downward

The CE penetrates a nuclear processed zone

Products of nuclear burning are carried to the surface • they can be observed

• return to the ISM via mass loss

1st D-up 2nd D-up 3rd D-up

Phase: RGB E-AGB TP-AGB

Products Central Shell of H-burning H-burning

H and HeShell burning

Dredge-ups

1 M

14N 12C 16O

14N 12C 16Os-process

4He 14N 12C 16O

1st D-up

2nd D-up

3rd D-up

The 2nd Dredge-up STOPS the C-O core mass growth

AGB phaseConvective Envelope

H-shell

He-shell

3 M

5 M

2nd D-up

Main growth E- AGB Still increases TP-AGB

TPs

CO core

The CO Core

E-AGBMCO He shell

TP-AGBMCO ~ cte

TP-AGB

TPs He shell pulses H shell

He-shellH-shell

ConvectiveEnvelope

C-OHe

H

Observed Mass Distribution of WDs

Napiwotski, Green, Saffer 1999

0.6 M 2 WDs 1.1 M

Samples

O-Ne WDs ??

Weidemann 2000

15 WDs 1.1 M Vennes, 1999

Mergers ??Segretain et al 97

2 WDs 1.4 M Napiwotski et al. 2006

The C-O Core Mass

Core Mass at He ignition Core Mass at 1st TPs

Cb

2nd D-up

He-core

CO-Core

Domínguez et al. 1999

Semiempirical Initial to Final Mass Relation

••

••

••

•

Herwig 1995

• Weidemann 2000Weidemann 1987

—

our models

––

New Data Mi Mf

Hyades

(Hipparcos) 3 0.68

NGC 3532

PG 0922+162 4 0.80

Single-valued Mi Mf

TPs

Few TPs

CO core growth during TP-AGB phase

How Long is the TP-AGB phase ??

Convective envelope

H-shell

He-shell

COM ~ 10-7 M/yr

5 106 yr MCh

Strong Mass Loss observed !!!

5 M

CO core

10-7 — 10-4 M/yr

s-process in AGB starsThe Neutron Source

22Ne(,n)25Mg

nn > 3-5x108 cm-3

nn < 107 cm-3

M < 3-4 M

M > 4 M

13C(,n)16O

T ~ 90 106 K

T > 300 106 K

For comparison, r-process (SNII ?) nn ~ 1022 cm-3

Constraining observationally the neutron density from abundances of

Rb vs. Sr, Y, Zr22Ne(,n)25Mg 13C(,n)16O

Mass: 4 – 8 M 3 M

85Kr

T n T n

10)Rb(

)Rb(87

85

-2 -1.5 -1 [Fe/H] 0 0.5

1.5 M

5 M

Low Mass !!

s-process elements

© Lattanzio

22Ne(,n)25Mg

2 Thermal Pulses

C/O

STARTING PARAMETERSSTARTING PARAMETERS

M = 2 M

[Fe/H]=0

but....Z = Z

αmixing length = 1.9Heini = 0.27

• Calibration of the SSM (Standard Solar Model) with the new composition• New determination of solar C, N and O (Allende-Prieto et al. 2002, Asplund et al. 2004):(Allende-Prieto et al. 2002, Asplund et al. 2004):

Zini 0.015

MASS-LOSS in our code

UP TO EARLY-AGB PHASE

AGB PHASE

REIMER’S MASS-LOSS(η=0.4)

• Fit to observational data of Whitelock et al. (2003)

and derivation of dM/dt=f (Period)• Period-Luminosity relation by Feast et al. (1989)

log dM/dt

How we treat the convection

• Schwarschild criterion: to determine convective borders

• Mixing length theory: to calculate the element velocities inside the convective zones

•At the boundaries we At the boundaries we assume that the velocity assume that the velocity profile drops, following an profile drops, following an exponentially decaying lawexponentially decaying law

v = vbce · exp (-d/β Hp)• Vbce is the convective

velocity at the inner border of the convective envelope (CE)

• d is the distance from the CE

• Hp is the scale pressure height

• β = 0.1WARNING: vbce=0 except during Dredge Up episodes

Efficiency of the mixing: we take it proportional to the ratio between the convective time scale and the time step of the calculation (Spark & Endal 1980)

THE NETWORK

About 500 isotopes

More than More than 700700 reactions reactionsfully coupled withfully coupled with

the physic evolutionthe physic evolution

Reactions Reference(n,γ)

(n,p) and (n,α)p and captures

beta decay

Bao & KaeppelerKoehler,Wagemans

NACRETakahashi&Yokoi

The TP-AGB PhaseThe TP-AGB Phase

ACTIVATIONOF THE

13C(α,n)16O reaction

First formationof the 13C-pocket

2 M

Z=Z

Low Mass

3rd D-up

Formation of the 13C-pocket (4th pulse with TDU)

13C

12C

14N

H12C(p,)13N

13N(+)13C

13C(,n)16O

Poison

14N(p,)15O

First TDU episode andconsequent 13C-pocket

formation

THE TP-AGB PHASETHE TP-AGB PHASE

M=2M

Z=Z

(Z=1.5x10-

2)C/Oini=0.54

Engulfment of the 13C-pocket in theconvective shell

Radiative burning of13C(,n)16O reaction

C/O=1C-star

C/O~2

Convective envelope

C-O core

DISK STARS

Mass Loss !!!

1th TDU episode:

Strong neutron flux, but too short timescale

2th TDU episode

Sr, Y,Zr

Cd, Pd, Sn

Ba group

Eu

Hf, Ta, W, Pb

Surface enrichment during TPs + DUP

ls1st peak

hs2nd peak

3rd peak

,

,loglog

Fe

El

Fe

El

N

N

N

N

Fe

El

TP-AGB phase: some numbers...Pulse

(with TDU)MTOT

(M)MH

(M)

ΔMTDU

(10-3 M)

ΔtINTERP

(105 yr)

C/O

1 1.901 0.561 0.4 1.52 0.33

2 1.894 0.568 1.5 1.77 0.36

3 1.878 0.575 2.5 1.68 0.46

4 1.843 0.583 3.5 1.60 0.61

5 1.771 0.590 4.4 1.52 0.82

6 1.650 0.596 4.2 1.43 1.06

7 1.457 0.603 4.7 1.33 1.36

8 1.196 0.609 3.5 1.21 1.67

9 0.923 0.615 0.07 1.05 1.67

Comparison with Galactic Carbon C(N) Stars

ObservationsAbia et al. 2002

s-processSurface C/O=1Z ~ Z

hs: Ba La Ce Nd Smls: Sr Y Zr

FRANEC2M 6th TP with TDU

Intrinsic C-stars Abia et al 2001

Toward lower metallicities Z=10-4

1

10

5

…

C-starLead-star

Observations (14 )

[Fe/H]~-2.2

0.4<[ls/Fe]<1.30.9<[hs/Fe]<2.31.9<[Pb/Fe]<3.3

Extrinsic Dilution

2M

Z=10-4

[ls/Fe]~1.7

[hs/Fe]~2.3

[Pb/Fe] ~ 3.1

Aoki et al. 2002Barbuy et al. 2005Cohen et al. 2003Van Eck et al. 2003

HALO STARS

Pulse by pulse surface enrichments

Comparison with LEAD (Halo) stars

(Van Eck et al. 2003)[Fe/H]=-2.1

McClure & Woodsworth, 1990

ORBITAL PARAMETERS !!

EXTRINSIC AGB

REQUESTED DILUTION

iniCOMPENV

trAGB

M

M

Murchison, Australia 1969

EARLY SOLAR SYSTEM SHORT RADIOACTIVITIES

Measured radioactivities, lifetimes, abundance ratios in ESS

.

Rad.(R)

.

Ref. (S)

.

(Myr)

.

Observ. Ratio

26Al

27Al

1.03

5x10-5

36Cl

35Cl

0.43

1.4x10-6

41Ca

40Ca

0.15

1.5x10-8

53Mn

55Mn

5.3

2.3x10-6 – 6x10-5

60Fe

56Fe

2.2

4x10-9 (PD)

107Pd

108Pd

9.4

2.0x10-5

129I

127I

23

10-4 146Sm

144Sm

148

0. 005

182Hf

180Hf

13

2.0x10-4

244Pu

238U

115

0.007

• INTEGRAL data imply ~ 2.8 M of live 26Al, of which ~ 2 M

come from massive stars (Limongi, Chieffi 2006). A further contribution of up to 1 M in a diffuse background (from AGBs and novae?) cannot be excluded (Lentz et al. 1999).

•The ISM 26Al/27Al=8.4 10-6 ratio is 5 times smaller than in the ESS. 

•This confirms a late contamination by a local source, in the collapsing cloud (e.g. stellar winds from the early Sun) or very close to it (e.g. a close-by nucleosynthesis event in a dying star). The nature of the source must still be decided (SN or AGB).

Measurements from INTEGRAL

AGB 26Al, 60Fe, 41Ca, 107Pd

Several sources required

Radioactivities & AGB Stars Production sites of short lived radioactive isotopes

.

Rad.

.

Stable

.

MS, Type II SN

.

Type Ia SN

.

LMS, IMS (AGB)

.

PR/PS

26Al

27Al

H-shell, expl. Ne

expl. Ne

H-shell, HBB

0.004;.0.001 – 0.05

36Cl

35Cl

s-process O-burn

?

s-process

0.006; 0.0016

41Ca

40Ca

s-process O-burn

?

s-process

0.006 - 0.003

53Mn

55Mn

expl. Si, NSE

NSE -------------------

0.1 < 0.1 ---

60Fe

56Fe

s-process, nNSE

nNSE

s-process

3x10-5 - 0.01-3x10-4

107Pd

108Pd

s- and r-processes

?

s-process

0.6 - 0.007

129I

127I

r-process

? ---------------------

1.4 ----- 146Sm

144Sm

p-process

p-process ---------------------

0.1 -----

182Hf

180Hf

r- or n-processes

?

(s-process)

0.21 – (3.5x10-4)

244Pu

238U

Extreme r-process

?

----------------------

0.7 -----

EARLY SOLAR SYSTEM SHORT RADIOACTIVITIES

lower mass 1.3M

Measured

26Al/27Al5 10-5

1.03 Myr

41Ca/40Ca1.5 10-8

0.15 Myr

60Fe/56Fe4 10-9

2.2 Myr

107Pd/108Pd2 10-5

9.4 Myr

M=2M

Z=Z

2 parameters

s-process nucleosynthesis vs. [Fe/H] Models: Travaglio et al. 2004

Draco

Sgr dsph

SMC

Carina

SculptorUMi

1st peak

2nd peak3rd peak

• Known distances• Dependence of Mixing and Nucleosynthesis with Z

B30 C1

C3

[hs/ls] vs. [Fe/H]

SMC

Galactic

SgrTheoretical PredictionConfirmed !!

But Observed C/O ~ 1 !!!Models C/O >>

Observed 12C/13C too low vs modelsde Laverny et al. 2006

hs: Ba La Nd Smls: Sr Y Zr

Sgr

Extramixing-CBPduring the interpulse period

Needed for:- 12C/13C - 17O/18O/16O-26Al in grains-7Li Does not alter AGB structure and evolutionBUT: 2 free parameters!

log (Li)=3.5±0.4

2

Domínguez et al. 2004

Nollett et al. 2003

Observed in Draco 461 [Fe/H]~ -2

Physical Mechanism ????

STD

CBP

Synthetic fit to D461 spectrum

4.2 m WHT+ ISIS, Roque de los Muchachos

Teff ~ 3600 K[Fe/H]=-2.0±0.2C/O=3-5log g= 0=2.5 km/s

log (Li)=no Li 1.5 3.0 3.5

R ~ 6500 IRAFS/N ~ 60

Best fitLiI

CaI

Model Atmospheres

SAM12 (Pavlenko 2003)

7Li Production in

3He(,)7Be T> 20-30 106 K

7Be(e-,)7Li 1/2 ~ 29 yr (T~ 25 106 K)

7Li(p,)4He T> 2 106 K

Cameron-Fowler belt Mechanism

HBB in Intermediate-Massive

mixing < 1/2 (7Be + e-)

Low mass Extra-mixing or CBP

Wasserburg, Boothroyd, Sackmann 1995Nollet, Busso, Wasserburg 2003

Luminosity – Core Mass

Constraints to D461 Mass

M < 2.0 M

Occurrence of 3rd D-up

M > 1.3 M

D461: Mv = -2.74±0.14(Shetrone et al. 2001)

& AGE

> 1 Gyr< 3 Gyr

Menv > 0.4-0.5 M

(Straniero et al. 2003)

M > 1.3 M AGE < 3 Gyr

Recent formation in Draco

C/O 12C/13C [Ba/Fe] Teff g 1.5 M Z=3 10-4

Z=0 4 – 8 M

H burning PP chains CNO cycle + 3

The first AGB stars

6-8 M

CNO

NormalTPs

He C

O N

T

Chieffi, Domínguez, Limongi, Straniero 2001

SDU 4-5 M Convection HCE

SDU

TDU

Contribution of the first AGB stars to the chemical Evolution of the Early Universe

Observations: IGM abundances (Ly-) [C/H] > -2.4

and halo [Fe/H] -2.5 [C,N/ Fe] > 1 EMP C-

Z=0 IMF & yields 4 –100 M

Z=0 YIELDS 4 – 8 M

• IMF 4-7 M

[C,N/ Fe] > 1

• rem<0.001 b

IMF

Abia et al. 2001 Chieffi et al. 2001

IMFNakamura & Umemura Yoshii & SaioSalpeter

Final Remarks•The main component and the strong component of the s- process (85 A 210) can be explained in a unique scenario: low mass AGB stars of different metallicities. Neutron captures are dominated by the 13C(,n)16O

• Galactic AGB C-stars confirm this picture

• Extragalactic AGB C-stars show the expected dependence of the s-process with metallicity

• Problems to reproduce the observed low C/O & 12C/13C in metal poor AGB stars rich in s-elements

• Extra-mixing is needed to explain 7Li in Li-rich AGB C- also explain 12C/13C, 16O/17O/18O & 26Al

But … Physics of extramixing ??

Final Remarks Why the observed C/O in AGB C-stars (metal poor) is low ?? Dust ?? Condensation ?? Huge DUP ?

Presolar grains: isotopic compositions have confirmed the general picture and the need of extramixing

Solar System formation: an AGB of low mass ~ 1.3 M contaminated the collapsing cloud in short radioactivities (work in progress)

The first AGB stars (Pop. III) enriched the IGM with metals, relevant for C and N !!!

Open problems in the simulations

Mixing regions Convection (1D mixing-length !! 3D ??) DUP (Hydrodynamics ??) Extra-mixing CBP (Physical Mechanism ?)

Mass-loss When the AGB ends Number of TPs

Huge effect on yields

AGB simulations take a lot of CPU 1 model 1 month parameters !!!!

Most relevant for Chemical Evolution

Around half of the Galactic 12C

Main and Strong component of the s-process 85 < A < 210 coming from Low Mass AGB stars of different Z

Crafoord Prize, 1986

The beauty of science is that nature will tell you when you are wrong. So will your colleagues,

but they may not always be right!

Jerry Wasserburg