Evidence of a late weak r-process

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Evidence of a late weak r-process
Fernando Montes
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Outline

• Motivation
• Missing abundances

• Reaction network calculations
• Results
• Conclusions

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Motivation contributions
log e log10 (Yel/YH)12
Ba
Eu
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Observations
Z47
Z38
Metal poor stars old stars
Ba/Eult0 Eu/Fegt0.3
R-process rich
Dloge loger-solar - logestar
Additional process to create residual abundances
!!
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Reaction network
Residuals YRESYsolar-Ys-Yp-Ystar
Astrophysical conditions T temperature ? nn
neutron density ? t neutron flux duration ?
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Reaction network

• Reaction network with classical neutron
  exposures
• Theoretical and experimental rates (REACLIB)
• Fast decay mode no neutrons, only beta decays
• Iron seed

nn1015 cm-3 T0.7 GK
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Results
To find the closest abundance pattern
r-process
s-process
Half-lives determine speed of the process
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Analysis
Ba
Pd
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Results
s-process
r-process
Neutron capture processes with a high neutron
density gt 1016 cm-3 best fit the residual pattern
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Results
Good agreement ! Late weak r-process
Scatter Sr, Y and Zr but Problems with the
s-process contribution
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Summary

• Residual abundance pattern is consistent with an
  r-process network calculation
• In the proposed scenario the strong r-process
  creates the majority of the elements
• The weak r-process occurs later and creates
  elements up to Z52-54
• There is scatter in the Sr, Y, Zr abundance
  which indicates that maybe the weak r-process is
  not as uniform as the strong r-process but the
  contribution from the s-process is still model
  dependant

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Collaborators
Michigan State University T. Beers T. Elliot H.
Schatz
Univ. of Mainz K. Farouqi, K.-L.
Kratz Karlsruhe M. Heil Univ. of Oklahoma J.
Cowan Univ. of Torino R. Gallino