AGB stars Inma Dominguez Sergio Cristallo Oscar Straniero.
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Transcript of AGB stars Inma Dominguez Sergio Cristallo Oscar Straniero.
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