1. Stellar Nucleosynthesis s-Process in Massive Stars
Mounib El Eid
American University of Beirut (AUB)
Department of Physics

2. Physics department
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4. outline
Introduction
2. Stellar Models
s-process results
what else?

5. We are made from star dust
1. Introductory Comments:
Except of the light elements :
1H, 2H, 3He, 4He ,7Be, 7Li
All other elements and isotopes were mainly made by nucleosynthesis in stars during their evolution and are expelled during the end stages of the stars.
These end stages are:
White Dwarfs
Neutron Stars
Black Holes
 Stellar nucleosynthesis drives the evolution of stars toward these end stages
 Stellar nucleosynthesis determines the nuclear energy production in stars
and this is what determines their lifetime.
Without nuclear energy and gravity:
no stars no elements no human beings
We are made from star dust

6. stars must convert H to He in their interior.
Interesting point:
stars must convert H to He in their interior.
However, most interstellar helium is of primordial origin. Why?
Two reasons:
(a) little mixing from the center to the surface of the star,
(b) helium is processed into heavier elements during the star’s evolution
Red
giant
Star
now
Supernova
1987
ongoing
cycle
Star-forming
nebula
Supernova
Remnant

7. A big Q
Supernova Remnant E from Radio to X-Ray 40 light years across, 190,000 light years away in the Small Magellanic Cloud

8. Expansion at 4 million miles/hour
Kepler's supernova
from NASA's Spitzer Space Telescope, Hubble Space Telescope, and e Chandra X-ray observatory
Expansion at 4 million miles/hour

9. Planetary Nebula
The Helix Nebula from La Silla Observatory
700 light years away
Will our Sun look like this one day?

10. Where are the elements made?
Iron

11. IRON Think: iron abundance high due to its high binding energy/nucleon
Mass Number
U=cosmological x=cosmic rays (spallations) H=hydrogen burning
H=helium burning C=carbon burning O=oxygen burning
S=silicon burning E= nuclear statistical equilibrium and r, s, p processes

12. Distribution of thee Heavy Elements r, s and p
abundance curve of heavy elements: solar system

13. Proton Number Neutron Number Chart of Nuclides; For orientation N =Z
 decay
+ decay
Proton Number
Proton addition
Neutron addition
-- decay
Neutron Number

14. Basics of the s-process
Seed nucleus: Iron
Neutron source C(,n)16O AGB stars
22Ne(,n) 25Mg Massive Stars
Neutron spectrum Maxwell-Boltzmann Distribution (details later)
Temperature range (25 – 30) KeV or (1.5 – 3.5) x 108 K Helium Fusion
( 90 – 100) KeV or ( )x 109 K Carbon Fusion
Time scale
Beta-decay much faster, Helium fusion
Comparable time scale: carbon fusion
Massive Stars
Thermally pulsating stars (AGB stars
Where?

15. How does the s-process works, in principle
69Ga 31 s s s s s 30 Z
64Zn
65Zn
66Zn
67Zn
69Zn
70Zn
68Zn s s 29
63Cu
64Cu
65Cu
66Cu s s s s 28
60Ni
61Ni
62Ni
63Ni
64Ni
65Ni s 27
Black: stable (s)
59Co
60Co s s s
Red: radioactive (R ) 26
56Fe
57Fe
58Fe
59Fe N

16. 3.2 Details of the s-process ( Ns – curve)
The s-process works with thermal zed neutrons. They undergo elastic scattering in the star’s plasma.
The neutrons obey the Maxwell-Botzmann distribution (MBD):
From lab experiments, we know that the neutron-capture cross section varies like:
S-wave scattering
MBD
E0 =most probable energy En
E0=kT

17. Thermal velocity of the neutron:
Due the the above energy dependence:
Let:
Maxwell folded
Then:
Implication: measurement of  near vT very useful.

18. Time variation of abundances: (Z+1,A)
Radioactive
(Z.A) Z N
(Z,A-1)
A+1
A -1 A
with
n = neutron flux
Beta-rate
in stellar plasma
(1)
Creation
destruction

19. (Time-integrated neutron flux)
define neutron exposure:
Using
in Eq. (1)
Using:
Every radioactive
nucleus beta-decays
Self-regulating equation with a steady-state solution:
This says: a nucleus with small  would have small abundance and a nucleus with high  would have large abundance.

20. Verification of
 Ns (Si=106 ) (mb)
Weak component
Massive stars
Main component, AGB stars

21. Tellur - Isotopes
Verification of the
With the Te-isotopes
122
123
124
125
126 Te sr s s s sr
121
123
s: s-only
r: r-only
Sr: both Sb sr sr
124
122
120 Sn sr r r
R-process path
Advantage of the  N-curve:
(b) Obtain average neutron flux and temperature
( c) analyze branching
(a) To obtain r-abundances: knowing  for an isotope , then Ns from the curve and Nr =N-Ns

22.  Ns (Si=106 ) (mb)
Branching

23. Stellar Models of Massive Stars
Recent review on this subject:
Mounib El Eid, Lih-Sin The & Bradley Meyer:
Space Science Review, 2009, online
In the folowingI will present :
Effect of the 12 C(,) 16 O rate
on the evolution including advanced stages
(2) Compare different calculations

24. Survival of and
If 12C(,) would be too effective, no oxygen would survive.
But this reaction is very important !!

25. The
reaction
Energy levels above and near the threshold of 12C(,) .
For temperatures T9=1.0 and above, the effective stellar energy is near E0=0.30 MeV (Gamow peak).
This energy is reached by the low energy tail of the resonance centered at 2.42 MeV (center of mass energy):
Two other sub-threshold resonances:

26. Several evaluations of
He burning;15-30 MSun
CF85: Caughlan et al ; 1985 , At. Data Nucl. Data Tables, 32, 197
Kunz: Kunz etal. : 2002, APJ, 567, 643
NACRE: Angulo et al , Nucl. Phys. A, 656, 3
Buchmann: 1996, APJ, 468, L127

27. Details of the stellar models

28. Hertzsprung-Russell Diagram

29. Energy equation: (Strong, weak, EM interaction
and gravitational. interaction)

30. see
El Eid, Meyer, The
APJ 285, 1994
CONVECTIVE
Note that the energy production does not comprise the whole convective core
NACRE
NACRE
The, El Eid, Meyer:
APJ, 533 (2007)

31. Imbriani et al (2001), ApJ 558, 903
Rate of
25 Msun star
CF85 > CF88
CF85
X 12=0.18
No convective
carbon-burning
core
X12 lower
Remaining
car bon mass fraction
No convective core
CF88
X12=0.42
But here

32. No convective carbon-burning
core
Woosley, Heger &Weaver (2002)
Rev .Mod. Phys. 74, 1015

33. s-process calculations
(a) 22Ne(,n) rate
(b) S-process in central helium burning
(c ) S-process in C-shell brning

34. 14N(, ) 18F(e+, ) 18O (, ) 22Ne(,n) 25Mg
Central He-burning
NACRE rate smaller than that of CF88 up to T8=2.4
14N(, ) 18F(e+, ) 18O (, ) 22Ne(,n) 25Mg
This happens at begin of central helium burning.
This becomes effective near end of central He-burning

35. s-process in core He-burning
25 M, solar-like initial compositionn
Neutron Density
Temperature
central
Helium mass fraction
exposure
overabundance
25C: CF88
for
25N: NACRE
CF88
22Ne(,n) release neutrons earlier in He-burning
neutron exposure  larger which leads to larger overproduction of 80Kr
It does not help to have higher neutron density as in 25N, since this
happens late in helium burning

37. Results for core He-burning

38. (X/X)Kr80 25C 25K 25N R91 pig09 618 183 174 481 232 Pignatari
et al (2009)
CF88
Kunz et al
NACRE
Raiteri
et al (91)
CF88
NACRE
 S-process production in this phase not sensitive top 12C(,)16O
 S-process reduced with the NACRE’s rate
The neutron poisoning reaction 16O(n,)17 O with
=34 barn at 30 KeV (Igasdhira etal 1995)
reduces the 80Kr overabundance by a factor of about 1.8.
 s-process in core He-burning is less efficient than found before

39. S-process in Carbon-Shell burning
The, El Eid, Meyer: APJ, 533 (2007)
Pignatari, Gallino, Heil, Wiescher, Kaeppler, Herwig, Bisterzo 2009 in press
Raiteri etal (1991),ApJ 367, 228

40. NACRE

41. Evolution through core Ne-burning phase under different assumptions
Central temperature evolves differently under different assumptions.
In 25 K: larger central Ne mass fraction evolution at lower TC but higher C

42. S-Process in Carbon shell-burning
Somewhat surprising results and very complicated issue
25 K
Kunz et al for C12(,)
Peak value

43. NACRE rate of C12(,)
25N
Peak value
3 episodes

44. History of the s-process in the star
Central He-burning
Carbon-Shell
Helium
shell
Neutron exposure (not averaged):

48. End He-burning C-Shell Burning
Pignatari Ra91a The et al. P/T M2, T9=1.05) (25N) (25K)
23Na
65.8
84.6
53.8
1.22
382
235
315
27Al
2.1
---
1.16
1.8
140
103
143
37Cl
64.8 --
72.1
0.9
65.6
61.1
61.8
40K
260
291
268
0.97
137
224
255
50Ti 20
15.9
15.8
1.27
21.6
16.9
16.4
54Cr
14.6
16.5
16.8
0.87
58 Fe
77.2
84.2
105
0.73
55.5
92.8
93.1
59Co
29.9
35.9
36.4
0.82
49.1
39.2
45.5
61Ni
59.9
60.4
67.9
62Ni
53.7
49.9
31.6
1.7
62.5
34.4
36.6
64Ni
166
164
56.6
2.9
221
109
115

49. 63Cu
134
91.8
58.3
2.3
179
11.5
64.6
65Cu
317
226
122
2.6
224
83.5
148
64Zn
36.8 41
29.4
1.25
4.7
8.6
23.2
66Zn
88.7
118.9 57
1.55
107
62.1
80.6
67Zn
127
171.7
79.4
1.6
272
137
160
68Zn
121
164.7 70
1.72
250
128
131
70Zn
0.3
0.38
0.79
21.7
39.9
70Ge
193
253.7
1.8
421
217
216
72Ge
114
190.7
72.2
1.58
246
187
158
73Ge
128.8
45.1
2.37
381
180
147
74Ge
94.2
99.3
35.9
2.62
251
101
84.9
75AS
60.2
59.6
26.3
2 .29
205
99.1
75.4
76Se
133
212.2
74.7
1.79
333
189
164
80Se
1.9 --
1.21
95.8
54.7
56.3
80Kr
232
480.7
174
1.33
169
124
181
82Kr
108
210.3
73.4
1.47
86Kr
0.80
----
2.57
0.31 73
50.9
10.4
87Rb
1.26
0.63
55.4
43.3
86Sr
147.3
57.1
1.87
103
20.7
138
87Sr
91.4
129.9
47.3
1.93
46.8
28.3
88Sr
26.8
34.8
14.1
39.8
20.1
27.7
96Zr
0.1
---
0.19
0.53
20.9
11.3
1.18

50. Summary of the results for the s-process
Efficiency of the s-process during core He-burning
is not sensitive to the 12C(,)16O reaction
But sensitive to the
22Ne(,n)25Mg and 16 O(n,)17O reactions
(2) Given the present situation, the efficiency of the s-process in massive stars
seems to significantly reduced.
(3) The s-process in carbon shell-burning depends crucially on the evolution of
the star during core helium burning and the following core carbon burning.
It is therefore influenced by the xxx
12C(,)16O rate.
Interesting: if this rate leads to relatively low mass fraction of carbon at the end
of core helium burning , then the s-process occurs later in time,
eventually after core Ne-burning.
The neutron density achieved is high and the nuclear reaction flow
reaches the zirconium region. Otherwise only the Sr region is
reached
(4) 86 Rb is produced during C-shell burning
(5) We estimate: massive stars may contribute at least 40% to the
solar–only nuclei with A<87

51. In He burning: no time to make errors
In C-shell more time for that

52. Concluding Thoughts
Nucleosynthesis shows us how the universe is well designed and balanced.
We (human being) struggle always to achieve balance in ourselves
 Stellar nucleosynthesis is driving force of the star’s evolution and a powerful tool to get insight into the internal structure of stars
 Stellar nucleosynthesis is a basic tool for understanding the chemical evolution of Galaxies
 Last not least we discover our cosmic connection through the elements that are made in stars. At least in this respect, it is a fascinating branch of Astrophysics.
END OF THE LECTURE: THANK YOU for your patience
It follows more details about the s-process and some rest material

53. Exotic s-process

54. Z=2x10-2 : Solar-like Z=10-3 red blue All this happen here
Convective
Envelope
All this happen here
blue
red
Z=10-3
No Convective Envelope

55. Z=10-3 Possible mixing of protons into the
helium shell. It works only at low metallicity.
Here: [Fe/H]=-4.5

56. Let’s believe it……… then
What is the advantage of this game?

57. If this would be true?, we make Primary Sr for example
Result after one time step of proton mixing into the helium convective shell.
Strong enhancement near Z=38 57

58. LEPP: Light Element Primary Process
These nuclei
(Fe-group up to the rising wing of the A=130-peak not reproduced in the supernova wind model
(Farouqi et al (2009).
They are not explained by the usual secondary ns-process.
Farouqi, Kratz, Mashonika, Cowan, Thielemann, Truran (2009)

59. Again: Elements with Z<38 are not produced together with those with Z> 38.
The conclusion so far:
The light trans-Fe-element are were not produced under the same conditions Eu.

60. Stop here

61. Stars with different initial metallicity
Observe:
For initial
stars do not evolve to red giant branch.

62. Convective zones of [Fe/H]= 0 25 Ms star
Solar-like composition
Convective zones of [Fe/H]= Ms star
Z=10 -3
Shaded areas are convective zones. Others are radiative

63. Lih-Sin is confusing us: he likes to mix in a most exotic way
Lih-Sin crashed the code
Possible mixing of protons into the
helium shell. It works only at low metallicity.
Here: [Fe/H]=-4.5

64. If this would be true?, we make Primary Sr
You have to be more interesting than right
Result after one time step of proton mixing into the helium convective shell.
Strong enhancement near Z=38 64

65. LEPP: Light Element Primary Process
These nuclei
(Fe-group up to the rising wing of the A=130-peak not reproduced in the supernova wind model
(Farouqi et al (2009).
They are not explained by the usual secondary ns-process.
Farouqi, Kratz, Mashonika, Cowan, Thielemann, Truran (2009)

66. Again: Elements with Z<38 are not produced together with those with Z> 38.
The conclusion so far:
The light trans-Fe-element are were not produced under the same conditions Eu.

67. r and s processes P s r rs

68. Path of R and S processes in Z-N Diagram

72. 1. Summary of the basic equations of stellar structure& evolution
Dependent variables: u= velocity r=radius T=Temperature
=density L=Luminosity P=pressure
Independent variables : M r =interior mass t=time
Spherical Symmetry is assumed,
1.Momentum equation:
(gravitational interaction)
2. Mass conservation
3. Definition of velocity:
4. Energy equation:
(Strong, weak & EM interaction )
5. Energy Transport
= mean opacity