AGB stars Inma Dominguez Sergio Cristallo Oscar Straniero

Evolution of Low & Intermediate Mass Stars M  8 M  C-O White Dwarfs M CO ~ 1.1 M   C ignition M MS = M UP ~ 8 M  Becker, Iben

Hertzsprung-Russell Diagram H central burning He central burning TP-AGB E-AGB RGB Pre Main Sequence FDU

AGB stars 12 C & 14 N Life cycles 7 Li (BBN) 26 Al (Early SS) s-elements main & strong component (88  A  210)  Thermal pulses  3 er 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 1989 Cameron 1982 SNII BBN SNII SNIa AGB SNII ? BBN Weak A<90 Main 90<A<204 Strong 204<A<210 Beyond Fe-peak: neutron captures 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) 26 Al 36 Cl 41 Ca 60 Fe 107 Pd (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% !!  7 Li (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 1 st D-up 2 nd D-up 3 rd D-up Phase: RGB E-AGB TP-AGB Products Central Shell of H-burning H-burning H and He Shell burning

Dredge-ups 1 M  14 N  12 C 16 O  14 N 12 C 16 O s-process  4 He 14 N  12 C 16 O  1 st D-up 2 nd D-up 3 rd D-up

The 2 nd Dredge-up STOPS the C-O core mass growth AGB phase Convective Envelope H-shell He-shell 3 M  5 M  2 nd D-up  Main growth E- AGB   Still increases TP-AGB TPs CO core

The CO Core  E-AGB M CO  He shell  TP-AGB M CO ~ cte TP-AGB TPs  He shell  pulses  H shell  He-shell H-shell Convective Envelope C-O He H

Observed Mass Distribution of WDs Napiwotski, Green, Saffer 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 ignitionCore Mass at 1 st TPs CbCb  2 nd D-up    He-core CO-Core Domínguez et al. 1999

Semiempirical Initial to Final Mass Relation Herwig 1995 Weidemann 2000 Weidemann 1987 — our models –– New Data MiMi MfMf Hyades (Hipparcos) NGC 3532 PG Single-valued M i M f    TPs Few TPs

CO core growth during TP-AGB phase How Long is the TP-AGB phase ?? Convective envelope H-shell He-shell ~ M  /yr yr M Ch Strong Mass Loss observed !!! 5 M  CO core — M  /yr

s-process in AGB stars The Neutron Source 22 Ne( ,n) 25 Mg n n > 3-5x10 8 cm -3 n n < 10 7 cm -3 M < 3-4 M  M > 4 M  13 C( ,n) 16 O T ~ K T > K For comparison, r-process (SNII ?) n n ~ cm -3

Constraining observationally the neutron density from abundances of Rb vs. Sr, Y, Zr 22 Ne( ,n) 25 Mg 13 C( ,n) 16 O Mass: 4 – 8 M   3 M  85 Kr T  n  T  n  [Fe/H] M  5 M  Low Mass !!

s-process elements © Lattanzio 22 Ne( ,n) 25 Mg 2 Thermal Pulses C/O 

STARTING PARAMETERS M = 2 M  [Fe/H]=0 but.... Z = Z   α mixing length = 1.9 He ini = 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): Z ini  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 assume that the velocity profile drops, following an exponentially decaying lawAt the boundaries we assume that the velocity profile drops, following an exponentially decaying law v = v bce · exp (-d/β H p ) V bce is the convective velocity at the inner border of the convective envelope (CE) d is the distance from the CE H p is the scale pressure height β = 0.1 WARNING: v bce =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) (n,p) and (n,α) p and  captures beta decay Bao & Kaeppeler Koehler,Wagemans NACRE Takahashi&Yokoi

The TP-AGB Phase ACTIVATION OF THE 13 C(α,n) 16 O reaction First formation of the 13 C-pocket 2 M  Z=Z  Low Mass

3 rd D-up

Formation of the 13 C-pocket (4 th pulse with TDU) 13 C 12 C 14 N H 12 C(p,  ) 13 N 13 N(  + ) 13 C 13 C( ,n) 16 O Poison 14 N(p,  ) 15 O

First TDU episode and consequent 13 C-pocket formation THE TP-AGB PHASE M=2M  Z=Z  (Z=1.5x10 -2 ) C/O ini =0.54 Engulfment of the 13 C-pocket in the convective shell Radiative burning of 13 C( ,n) 16 O reaction C/O=1 C-star C/O~2 Convective envelope C-O core DISK STARS Mass Loss !!!

1 th TDU episode: Strong neutron flux, but too short timescale 2th TDU episode Sr, Y,ZrCd, Pd, SnBa group Eu Hf, Ta, W, Pb Surface enrichment during TPs + DUP ls 1st peak hs 2nd peak 3rd peak

TP-AGB phase: some numbers... Pulse (with TDU) M TOT (M  ) M H (M  ) ΔM TDU (10 -3 M  ) Δt INTERP (10 5 yr) C/O

Comparison with Galactic Carbon C(N) Stars Observations Abia et al s-process Surface C/O=1 Z ~ Z  hs: Ba La Ce Nd Sm ls: Sr Y Zr FRANEC 2M  6th TP with TDU  Intrinsic C-stars Abia et al 2001

Toward lower metallicities Z= … C-star Lead-star Observations (14  ) [Fe/H]~ <[ls/Fe]< <[hs/Fe]< <[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 Barbuy et al Cohen et al Van Eck et al 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

Murchison, Australia 1969 EARLY SOLAR SYSTEM SHORT RADIOACTIVITIES

INTEGRAL data imply ~ 2.8 M  of live 26 Al, 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 26 Al/ 27 Al= 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  26 Al, 60 Fe, 41 Ca, 107 Pd Several sources required

Radioactivities & AGB Stars

EARLY SOLAR SYSTEM SHORT RADIOACTIVITIES lower mass  1.3M  Measured 26 Al/ 27 Al Myr 41 Ca/ 40 Ca Myr 60 Fe/ 56 Fe Myr 107 Pd/ 108 Pd Myr M=2M  Z=Z  2 parameters

s-process nucleosynthesis vs. [Fe/H]  Models: Travaglio et al Draco Sgr dsph SMC Carina Sculptor UMi 1st peak 2nd peak 3rd peak Known distances Dependence of Mixing and Nucleosynthesis with Z

B30   C1 C3  [hs/ls] vs. [Fe/H] SMC Galactic Sgr Theoretical Prediction Confirmed !! But Observed C/O ~ 1 !!! Models C/O >> Observed 12 C/ 13 C too low vs models de Laverny et al hs: Ba La Nd Sm ls: Sr Y Zr Sgr

Extramixing-CBP during the interpulse period Needed for: - 12 C/ 13 C - 17 O/ 18 O/ 16 O - 26 Al in grains - 7 Li Does not alter AGB structure and evolution BUT: 2 free parameters! log  (Li)=3.5±0.4 2 Domínguez et al Nollett et al 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 T eff ~ 3600 K [Fe/H]=-2.0±0.2 C/O=3-5 log g= 0  =2.5 km/s log  (Li)=no Li R ~ 6500 IRAF S/N ~ 60 Best fit LiI CaI Model Atmospheres SAM12 (Pavlenko 2003)

7 Li Production in   3 He( ,  ) 7 Be T> K  7 Be(e -, ) 7 Li  1/2 ~ 29 yr (T~ K) 7 Li(p,  ) 4 He T> K Cameron-Fowler belt Mechanism HBB in Intermediate-Massive   mixing <  1/2 ( 7 Be + e - ) Low mass  Extra-mixing or CBP Wasserburg, Boothroyd, Sackmann 1995 Nollet, Busso, Wasserburg 2003

Luminosity – Core Mass  Constraints to D461 Mass M < 2.0 M  Occurrence of 3 rd D-up M > 1.3 M  D461: M v = -2.74±0.14 (Shetrone et al ) & AGE > 1 Gyr < 3 Gyr M env > M  (Straniero et al. 2003) M > 1.3 M  AGE < 3 Gyr Recent  formation in Draco C/O 12 C/ 13 C [Ba/Fe] T eff g 1.5 M  Z=

Z=0 4 – 8 M  H burning  PP chains CNO cycle + 3  The first AGB stars 6-8 M  CNO Normal TPs 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 Chieffi et al IMF Nakamura & Umemura Yoshii & Saio Salpeter

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 13 C( ,n) 16 O 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 & 12 C/ 13 C in metal poor AGB stars rich in s-elements Extra-mixing is needed to explain 7 Li in Li-rich AGB C-  also explain 12 C/ 13 C, 16 O/ 17 O/ 18 O & 26 Al 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 12 C  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