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New Mechanisms for Beryllium
Production in Early Core-Collapse
Supernovae
Projjwal Banerjee (UC Berkeley)
with
Y. -Z, Qian (UMN), W. Haxton (UCB & LBL) and A. Heger (Monash U.)
Based on PRL 110, 141101 (2013)
Evolution of Be and B
Prantzos
Standard GCR scenario predicts secondary evolution
Does not match with observations
nu-process can account for primary B production (Woosley et al., 1990)
Modified GCR scenarios producing primary Be and B is still a matter of debate
Are there other sites for Be production?
Be form Core-Collapse Supernova?
1st Scenario
2nd Scenario
Models from Alex Heger
Can Neutrino interactions result in Be production?
Nucleosynthesis in He shell in both scenarios can make
Be.
Beryllium from Neutron-Capture
Neutral Current is not very
effective in neutron production.
Outer He Shell Low C, O poisons
PNS
Charged Current Reactions
sensitive to oscillations (MSW)
Inverted Hierarchy
Normal Hierarchy
Produces neutrons that are not reabsorbed
Destroys neutrons
Only IH can work!
Beryllium from r-process!
Low explosion energies result in fallback of inner
zones,
whereas Be in the He shell is always ejected!
Unlike the associated r-process can happen in
metal-free stars. Does not need pre-existing seed.
Can work without oscillations.
Be Production in CCSN
•Bulk material such as He remains unchanged as
the
shock temperature is low.
•Other light elements are dissociated and reassembled.
•Too much of C and O for neutron capture to
happen.
•However, steep density profile leads to very fast
expansion and cooling within ~4 s to below
T < 2.e+8 K where Be is no longer destroyed.
•Neutrinos are still around and produce Be via
Fast shock expansion and cooling due to steep density profile is the key.
Comparison Between the Two
Scenarios
Scenario 1
Be is produced in the He shell before the
passage of shock.
Scenario 2
Be is produced in the He shell after passage of
shock.
Sensitive to explosion energy. Be survives for
low explosion energy accompanied by
fallback.
Not very sensitive to explosion energy and all of
the ejecta comes out.
Happens via neutron capture in low metallicity
progenitors.
Has nothing to do with neutron capture. Can
happen
at metallicities (potentially).
Generally needs inverted mass hierarchy with
a hard spectra to produce enough neutrons.
Can
also work for soft spectra and in scenarios
without oscillation.
Relies on the steep density profile resulting in fast
expansion. Hard spectra and inverted hierarchy is
desirable but not necessary necessary. Can work
without oscillations.
Also the site for cold r-process in the He shell.
No associated r-process.
Be in Metal-Poor Stars
Boesgaard 2011, Smiljanic 2009, Tan 2009
Not expected to produce bulk Be in the Galaxy. However, can
account for Be in very metal poor stars.
Non-GCR Sources for Bulk Be Production
Neutron Star
Mergers?
Goriely, Bauswein & Janka (2011)
Summary
• Two new mechanisms related top CCSN was proposed to
produce
rare Be was discussed.
•The first mechanism is tied to the He shell r-process and works
only at [Z] <~ -3 for inverted hierarchy and preferably with a hard
spectra. Low explosion energy is required for Be to survive.
• The second mechanism works in low mass SN and is
independent of
metallicity. Less sensitive to neutrino parameters and explosion
energy. Can work at all metallicities.
• Cannot account for the bulk Be in the Galaxy but can explain Be
in
metal-poor stars.
• GCR and other mechanisms such as NSM can contribute to
primary
Be production and may be responsible for the bulk of Be
observed.
• Be may not be a pure GCR element as was previously thought.