AGB stars

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AGB stars
Inma Dominguez
Sergio Cristallo
Oscar 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
RGB
He central
burning
H central
burning
Pre
Main Sequence
FDU
AGB stars
Nucleosynthesis
75% of the mass return to the ISM
12C
& 14N Life cycles
7Li
(BBN)
26Al (Early SS)
s-elements main & strong component
(88  A  210)
Pieces of their envelopes  Meteorites
Not an
easy
phase
 Thermal pulses
 3er Dredge-up
 Mass Loss
 HBB
 Mixing process
 CBP
Solar System Abundances
BBN
SNII
AGB SNII
SNII ?
SNIa
BBN
AGB
AGB
Weak Main
Strong
A<90 90<A<204 204<A<210
Beyond Fe-peak: neutron captures
Anders & Grevesse 1989
Cameron 1982
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 ?
 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)
 Most extrasolar grains recovered in meteorites
 Pieces of AGB stars in terrestial laboratories !!
 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)
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
of
Central
H-burning
Shell
H-burning
H and He
Shell burning
Dredge-ups
1st D-up
2nd D-up
4He 14N

12C 16O 
3rd D-up
1 M
14N 12C
16O
s-process 
14N

12C
16O

The 2nd Dredge-up STOPS the C-O
core mass growth
AGB
phase
Convective Envelope
3 M
H-shell
He-shell
CO core
2nd D-up
5 M
TPs
 Main growth
E- AGB

 Still increases
TP-AGB
The CO Core
 E-AGB
MCO  He shell
TP-AGB
H
C-O
He-shell

He
H-shell
Convective
Envelope
 TP-AGB
MCO ~ cte
TPs
 He shell  pulses
 H shell 
Observed Mass Distribution of WDs
0.6 M
Samples
 2 WDs  1.1 M
Napiwotski, Green, Saffer
1999
 2 WDs 1.4 M
Napiwotski et al. 2006
 15 WDs  1.1 M
Vennes, 1999
O-Ne WDs ??
Weidemann 2000
Mergers ??
Segretain et al 97
The C-O Core Mass
Core Mass at He ignition
Core Mass at 1st TPs
Cb
He-core
2nd D-up



CO-Core
Domínguez et al. 1999
Semiempirical Initial to Final
Mass Relation
— Herwig 1995
•
•
•

TPs
•
•

––
•
•
•
Weidemann 1987
Weidemann 2000
our models
New Data
Mi Mf
Hyades
(Hipparcos)
3
0.68
NGC 3532
PG 0922+162
4
0.80
Single-valued
Mi  Mf
Few TPs
CO core growth
during TP-AGB phase
Convective envelope
M CO ~ 10-7 M/yr
How Long is the
TP-AGB phase ??
5 M
H-shell
He-shell
CO core
5 106 yr 
MCh
Strong Mass Loss
observed !!!
10-7 — 10-4 M/yr
s-process in AGB stars
The Neutron Source
22Ne(,n)25Mg
T > 300 106 K
nn > 3-5x108 cm-3
M > 4 M
13C(,n)16O
T ~ 90 106 K
nn < 107 cm-3
M < 3-4 M
For comparison, r-process (SNII ?) nn ~ 1022 cm-3
Constraining observationally the
neutron density from abundances of Rb
vs. Sr, Y, Zr
22Ne(,n)25Mg
13C(,n)16O
T  n  Mass: 4 – 8 M
T  n
 3 M
 (85 Rb )
 10
87
 ( Rb )
5 M
1.5 M
Low Mass !!
85Kr
-2
-1.5
-1
[Fe/H]
0
0.5
s-process elements
2 Thermal Pulses
C/O 
22Ne(,n)25Mg
© Lattanzio
STARTING PARAMETERS
M = 2 M
Z = Z
•
•

[Fe/H]=0

but....
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):
Heini = 0.27
Z  0.015 α
ini
mixing length
= 1.9
MASS-LOSS in our code
REIMER’S MASS-LOSS
(η=0.4)
UP TO EARLY-AGB
PHASE
• Fit
to observational data of
Whitelock et al. (2003)
and derivation of dM/dt=f (Period)
• Period-Luminosity relation by Feast et al. (1989)
AGB PHASE
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 assume
that the velocity profile drops,
following an exponentially
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 = 0.1
WARNING: 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 700 reactions
fully coupled with
the physic evolution
Reactions
Reference
(n,γ)
Bao & Kaeppeler
(n,p) and (n,α) Koehler,Wagemans
p and  captures
NACRE
beta decay
Takahashi&Yokoi
The TP-AGB Phase
Low Mass
First formation
of the 13C-pocket
2 M

Z=Z
ACTIVATION
OF THE
13C(α,n)16O reaction
3rd D-up
Formation of the 13C-pocket
(4th pulse with TDU)
12C
H
12C(p,)13N
14N
13C
13N(+)13C
13C(,n)16O
Poison
14N(p,)15O
THE TP-AGB PHASE
First TDU episode and
consequent 13C-pocket C/O~2
formation
C/O=1
C-star
Convective
envelope
C-O core
DISK STARS
M=2M
Z=Z
(Z=1.5x10-2)
C/Oini=0.54
Radiative burning of
13C(,n)16O reaction
Mass Loss !!!
Engulfment of the
13C-pocket in the
convective shell
Surface enrichment during TPs + DUP
3.0
3.5
2.5
3.0
2th TDU
Cd,episode
Pd, Sn
2.5
2.0
Sr, th
Y,Zr
[ [XX//FFee]]
1 TDU
Pb
Hf, Ta, W,
3rd peak
Ba group
hs
episode:
2nd peakEu
ls
1st peak
Strong neutron flux,
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0
but too short
timescale
-0.5
-0.5
5
55
15
15
15
25
25
25
35
35
35
45
45
45
ZZZ
55
55
55
65
65
65
7575
75
8585
85
 El 
 NEl 
 NEl ,  
 Fe   log  NFe   log  NFe,  
 




TP-AGB phase: some numbers...
Pulse
(with TDU)
MTOT
(M)
1
1.901
MH
(M)
0.561
2
3
4
5
6
7
8
9
1.894
1.878
1.843
1.771
1.650
1.457
1.196
0.923
0.568
0.575
0.583
0.590
0.596
0.603
0.609
0.615
ΔMTDU ΔtINTERP
(10-3 M) (105 yr)
0.4
1.52
1.5
2.5
3.5
4.4
4.2
4.7
3.5
0.07
1.77
1.68
1.60
1.52
1.43
1.33
1.21
1.05
C/O
0.33
0.36
0.46
0.61
0.82
1.06
1.36
1.67
1.67
Comparison with Galactic Carbon C(N) Stars
Z ~ Z
s-process
Surface C/O=1
Observations
Abia et al. 2002
FRANEC
2M 6th TP with TDU
hs:
Ba La Ce Nd Sm
ls:
Sr Y Zr
 Intrinsic C-stars
Abia et al 2001
Toward lower metallicities Z=10-4
Pulse by pulse surface enrichments
C-star
Lead-star
2M
Z=10-4
[Pb/Fe] ~ 3.1
[hs/Fe]~2.3
[ls/Fe]~1.7
…
10
5
1
HALO STARS
Observations (14 )
[Fe/H]~-2.2
0.4<[ls/Fe]<1.3
0.9<[hs/Fe]<2.3
1.9<[Pb/Fe]<3.3
Aoki et al. 2002
Barbuy et al. 2005
Cohen et al. 2003
Van Eck et al. 2003
Extrinsic  Dilution
Comparison with LEAD (Halo) stars
REQUESTED
DILUTION
[Fe/H]=-2.1
(Van Eck et al. 2003)
tr
M AGB
ini
M ENV
COMP
EXTRINSIC
AGB
ORBITAL PARAMETERS !!
McClure & Woodsworth,
1990
EARLY SOLAR SYSTEM
SHORT RADIOACTIVITIES
Murchison, Australia 1969
Measured radioactivities, lifetimes, abundance ratios in ESS
.
.
.
Rad.(R)
Ref. (S)
26
27
Al
36
41
53
 (Myr)
Observ. Ratio
1.03
5x10-5
Cl
35
Cl
0.43
1.4x10-6
Ca
40
Ca
0.15
1.5x10-8
Mn
5.3
2.3x10-6 – 6x10-5
56
2.2
4x10-9 (PD)
9.4
2.0x10-5
I
23
10-4
144
Sm
148
0. 005
Hf
13
2.0x10-4
U
115
0.007
Mn
60
Al
.
Fe
107
Pd
129
146
I
Sm
55
Fe
108
Pd
127
182
Hf
180
244
Pu
238
Measurements from INTEGRAL
• 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
ESS.
26Al/27Al=8.4
10-6 ratio is 5 times smaller than in the
•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).
Several
sources
required
AGB 
26Al, 60Fe, 41Ca, 107Pd
Radioactivities & AGB Stars
Production sites of short lived radioactive isotopes
.
.
.
Rad. Stable
26
Al
s-process O-burn
?
s-process
0.006; 0.0016
Ca
s-process O-burn
?
s-process
0.006 - 0.003
Mn
expl. Si, NSE
NSE
s-process, nNSE
nNSE
s-process
s- and r-processes
?
s-process
0.6 - 0.007
Ca
40
Mn
55
Pd
129
146
I
Sm
182
Hf
244
Pu
PR/PS
Cl
41
107
Type Ia SN LMS, IMS (AGB)
H-shell, expl. Ne
35
Fe
.
Al
Cl
60
MS, Type II SN
.
27
36
53
.
56
Fe
108
Pd
127
144
expl. Ne
H-shell, HBB 0.004;.0.001 – 0.05
-------------------
0.1 < 0.1 --3x10-5 - 0.01-3x10-4
I
r-process
?
---------------------
1.4 -----
Sm
p-process
p-process
---------------------
0.1 -----
180
Hf
238
r- or n-processes
?
(s-process)
U Extreme r-process
?
----------------------
0.21 – (3.5x10-4)
0.7 -----
Measured
EARLY SOLAR SYSTEM
SHORT RADIOACTIVITIES
26Al/27Al
5 10-5
1.03 Myr
M=2M
Z=Z
41Ca/40Ca
1.5 10-8
0.15 Myr
60Fe/56Fe
4 10-9
2.2 Myr
107Pd/108Pd
2 parameters
2 10-5
9.4 Myr
lower mass  1.3M
s-process nucleosynthesis vs. [Fe/H]
 Models: Travaglio et al. 2004
1st peak
• Known distances
• Dependence of
Draco
Mixing and
Nucleosynthesis
with Z
SMC
Sgr dsph
Carina
UMi
3rd peak
Sculptor
2nd peak
hs:
Ba La Nd Sm
ls:
Sr Y Zr
[hs/ls]
vs.
[Fe/H]
B30
SMC

 C1
Sgr
C3

Sgr
Galactic
de Laverny et al. 2006
Theoretical
Prediction
Confirmed !!
But
Observed
C/O ~ 1 !!!
Models
C/O >>
Observed
12C/13C too
low vs models
Extramixing-CBP
during the interpulse period
Needed for:
- 12C/13C
- 17O/18O/16O
-26Al in grains
-7Li
Does not alter
AGB structure
and evolution
BUT:
2 free
parameters!
Observed in Draco
461 [Fe/H]~ -2
log (Li)=3.5±0.4
CBP
2
STD
Nollett et al. 2003
Physical Mechanism ????
Domínguez et al. 2004
Synthetic fit to D461 spectrum
4.2 m WHT+ ISIS, Roque de los Muchachos R ~ 6500
IRAF
S/N ~ 60
Model Atmospheres
CaI
log (Li)=no Li
1.5
3.0
3.5
LiI
SAM12 (Pavlenko 2003)
Best fit
Teff ~ 3600 K
[Fe/H]=-2.0±0.2
C/O=3-5
log g= 0
=2.5 km/s
7Li
Production in 
Cameron-Fowler belt Mechanism
 3He(,)7Be
T> 20-30 106 K
 7Be(e-,)7Li
1/2 ~ 29 yr (T~ 25 106 K)
7Li(p,)4He
 HBB in Intermediate-Massive 
T> 2 106 K
mixing < 1/2 (7Be + e-)
Low mass   Extra-mixing or CBP
Wasserburg, Boothroyd, Sackmann 1995
Nollet, Busso, Wasserburg 2003
Constraints to D461 Mass & AGE
C/O
12C/13C
[Ba/Fe]
Teff g
Luminosity – Core Mass
D461: Mv = -2.74±0.14
(Shetrone et al. 2001)
1.5 M Z=3 10-4
Occurrence of 3rd D-up
Menv > 0.4-0.5 M
(Straniero et al. 2003)

M < 2.0 M
> 1 Gyr
M > 1.3 M
M > 1.3 M < 3 Gyr
AGE < 3 Gyr
Recent  formation in Draco
The first AGB stars
Chieffi, Domínguez, Limongi, Straniero 2001
Z=0 4 – 8 M
H burning  PP chains
CNO cycle + 3
6-8 M SDU
He
O
C
4-5 M
Convection HCE
CNO
N
SDU
T
Normal
TPs
TDU
Contribution of the first AGB stars to
the chemical Evolution of the Early Universe
Abia et al. 2001 Chieffi et al. 2001
Observations:
IGM abundances (Ly-) [C/H] > -2.4
and halo  [Fe/H]  -2.5  [C,N/ Fe] > 1 EMP C-
Z=0
Z=0
IMF & yields 4 –100 M
YIELDS 4 – 8 M
IMF
Nakamura & Umemura
Yoshii & Saio
Salpeter
IMF
• IMF 4-7 M
[C,N/ Fe] > 1
• rem<0.001 b
Final Remarks
•The main component and the strong component of the sprocess (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 &
metal poor AGB stars rich in s-elements
12C/13C
in
• 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
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
Crafoord Prize, 1986
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