study of the s-process in low mass stars of galactic disc metallicity
DESCRIPTION
Study of the s-process in low mass stars of Galactic disc metallicity. Laura Husti Roberto Gallino Sara Bisterzo. Outline: Origin of the heavy elements. Stellar Nucleosynthesis and Evolution. S-process nucleosynthesis in AGB stars at solar metallicity. - PowerPoint PPT PresentationTRANSCRIPT
Study of the s-process in low mass stars of Galactic
disc metallicity
Laura Husti
Roberto GallinoSara Bisterzo
2
Outline:Outline:
• Origin of the heavy elements. Origin of the heavy elements.
• Stellar Nucleosynthesis and Evolution.Stellar Nucleosynthesis and Evolution.
• S-process nucleosynthesis in AGB S-process nucleosynthesis in AGB starsstars at solar metallicity. at solar metallicity.
• Comparison with spectroscopic data of Comparison with spectroscopic data of intrinsic and extrinsic AGBsintrinsic and extrinsic AGBs
3
10-3
10-2
10-1
100
101
102
103
104
105
106
107
108
109
1010
1011A
bund
ance
rel
ativ
e to
10
6 sili
con
200150100500Mass number
Solar system abundances(at the time of solar system formation)
GH,He
(big bang)
Carbon (AGB stars)
Fe peak(mostly Type I SN)
N=82r-process peak
Te, Xe(Type II SN)
N=82s-process peak
Ba, La, Ce(AGB stars)
N-126r-process peak
Os,Ir,Pt(Type II SN)
N=126s-process peak
Pb,Bi(AGB stars)
ThUU,Th
(Type II SN)
-elements(mostly Type II SN)
4
Formation of Heavy Elements
• Thermonuclear reactions A<56
• Neutron captures - slow (s-process)105-1011 free
neutrons/cm3
- rapid (r-process) 1022-1025 free
neutrons/cm3
5
s-process
6
Stellar evolution of low mass stars• Core H burning• Core H exhaustion and
contraction of the star• H-shell ignition → core
contraction + envelope expansion
• First dredge-up• Core He burning• Core He exhaustion;
contraction of the C-O core
• Degenerate C-O core + alternate burning H and He shells + He intershell + extended convective envelope
7
Nucleosynthesis in AGB Stars• Neutron sources:
– radiative 13C(α,n)16O– convective 22Ne(α,n)25Mg
• 22Ne formation: 14 N(α,γ)18F(β+,ν)18O(α,γ) 22Ne• 13C formation: 12C(p, γ) 13 N(β+,ν) 13C(p, γ) 14 N
Busso, Gallino &Wasserburg ARA&A 1999
8
Variuos 13C pocket efficiencies, same metallicity
ls(Sr, Y, Zr)
hs(Ba, La, Cs, Nd,Sm)
Pb
9
IRAS 0713+1005
10
Extrinsic AGBs
21 1 2
2
2
1
1
tAGB
envini
envobs MMM
diltAGB
envobs
M
M10
dilFe
X
Fe
XAGB
dilFe
XdilFe
XobsAGBini
101010110log
11
HD 123585
Allen & Barbuy 2006
12
Conclusions
• comparison between theoretical models and spectroscopic observations for the element abundances of 30 barium stars and 12 post-AGB stars
• models succesfully reproduce the observational data