1. Mounib El Eid meid@aub.edu.lb Impact of Key Nuclear Reactions
on Stellar Structures & Nucleosynthesis
This is a sea view of the American University of Beirut
Mounib El Eid
Russbach: March 2015

2. I usually chose the beautiful.
A message
My work always tried to unite the true with the beautiful, but when I had to choose between one or the other,
I usually chose the beautiful.
Hermann Weyl

3. Outline blue loops of intermediate mass stars –CNO species 1. 2.
Massive star- s-process 3.
AGB stars –s-process 4.
It is a selection about which I know what I am talking about

4. The CNO cycle
Energy generation rate mainly controlled by this slowest reaction in the CN cycle: 1.
nuclear
Neutrino processes
near T= K

5. S-factor Reaction rate Level scheme in 15O NACRE
The S-factor used to get the C-rate is derived from R-matrix fit for the MeV and ground state transition, the recommended S-factor for MeV (Adleberger et al 2011), the LUNA fits for the weaker transition to the MeV and MeV states (Imbriani et al 2005).
LUNA/NACRE
Champagne/NACRE
C-rate
S-factor
Reaction rate

6. See next 😃 Effects on stellar evolution Summary:
shows complicated interplay of direct and resonant capture. The resonant capture involves a sub-threshold resonance at -504 KeV (Ex=6.791 MeV state in 15O), and a low energy resonance at Ecm=259 KeV and interference between the sub-threshold resonance and the higher excitation states
Effects on stellar evolution
See next 😃

7. 1 2 3 How are the loops initiated? N energy generation rate XH T
It is the enforcement of the H-burning shell which initiate the loop

8. Cepheid variables Effect of the Loops suppressed For M/Msun = 5-8
Loops recovered, how?
Cepheid variables

9. Recovering the blue loops
Through modified mixing
Z-=overshoot distance, in terms of pressure scale height Hp
The parameter f determines how fast D decreases

10. 6 Msun
Loop recovered (dashed line)
.core overshooting establishes higher T in the H-shell region, while envelope overshooting leads to deeper penetration of the H-profile.
Dashed line : overshoot distance od 0.1 Hp, loop recovered. T does not fall as rapidly as in case without overshooting
Solid line: no overshoot, loop suppressed

11. Overshoot distance from the edge of the core by 0
Overshoot distance from the edge of the core by 0.5 Hp suppresses the loop, slice the H-shell would operate. Not efficient H-shell burning to initiate the loop during core He-burning for this 6 Msun star

12. The
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:

13. Several evaluations of
He burning;15-30 MSun
CF85: Caughlan et al ; Atom.. Data Nucl. Data Tables, 32, 197 (1985)
Kunz: Kunz etal. APJ, 567, 643 (2002)
NACRE: Angulo et al , Nucl. Phys. A, 656, 3A, 1999
Buchmann: 1996, APJ, 468, L127 (1996)

14. Quantized collective charge oscillations in an ionized gas
Neutrino Processes
Quantized collective charge oscillations in an ionized gas
Like Compton scattering , but outgoing photon replaced by neutrinos.
Important in carbon burning

15. Carbon burning

16. see
El Eid, Meyer, The
APJ 611, 452 (2004)
The, El Eid, Meyer:
APJ, 655, 1058, (2007)
Dark areas: CONVECTIVE
Note that the energy production does not comprise the whole convective core
NACRE
NACRE

17. 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

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

19. 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

20. 25 M_sun

21. 25 M_un

22. S-process in massive stars (15 Msun and above) : main characteristics, sure about it
 In core He-burning, s-process rather sensitive to the reaction
s-process in Carbon-shell burning depends on the evolution of massive stars during core He-burning and the ensuing carbon burning. In particular, on the location of the carbon shells. This is related to the mass fraction of carbon (X12) determine by the
operating in late phase of core He-burning
If X12 is relatively low, the s-process occurs later during Ne-burning . This leads to higher neutron density in the range of 1011 n/cm-3. Consequently, some production of 90Zr is possible.
If X12 is relatively high (Kunz et al rate), then the s-process occurs earlier in the evolution (before Ne burning. Consequently, lower neutron density is achieved, and only the Sr-region is reached- that is amazing

23. AGB Stars and s-process
Concerning the s-process
In HR Diagram
“Cat Eye” planetary nebula
after the AGB phase

24. 5 M loop  2nd Dredge up end core  1st t Dredge up   4
Main sequence
End core
H-burning
Begin core
He-burning
2nd Dredge up
1st t Dredge up
Halabi, El Eid and Champagne (2012)
Recent work on blue loop:
1st dredge up: of H-burning
(He, 12C and 14N) to the surface
end core
He-burning 
 4

27. Thermal pulsations P-nucleus cannot be produced by the s-process
Role of

28. Overproduction factors of the IMF-averaged stars (15,20,25,30) Msun
Arlandini etal. (1999)
Main component
Solar
abundances
Weak
component
Massive
Stars
AGB Stars
Overproduction factors of the IMF-averaged stars (15,20,25,30) Msun

29. Challenging Figure Get in touch with chemical evolution
Galactic evolution of the r-process and the s-process I n terms of Lanthanum (La, mainly s-process) versus Europium (Eu, mainly r-process)
S-process stars already at [Fe/H] -=2.0, surprising.
Only r-process
Metallicity
Filled circles: halo stars
Diamond: disk stars
Simmerer et al, Apj, 167, 1091 (2004)

30. Conclusion
Reliable nuclear reaction rates are needed in stellar evolution
The most challenging problem in the study of stellar structure and nucleosynthesis is the treatment of mixing. Three-dim simulations are coming , a challenge topic for young researchers

31. 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
Electromagnetic interaction