New Mechanisms for Beryllium Production in Early Core-Collapse Supernovae

1. 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)

2. 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?

3. 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.

4. PNS Beryllium from Neutron-Capture Neutral Current is not very effective in neutron production. Outer He Shell Low C, O poisons Charged Current Reactions sensitive to oscillations (MSW) Inverted Hierarchy Normal Hierarchy Produces neutrons that are not reabsorbed Destroys neutrons Only IH can work!

5. 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.

6. Be Production in CCSN • Bulk material such as He remains unchanged as the • shock temperature is low. • Other light elements are dissociated and re-assembled. • 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.

7. Comparison Between the Two Scenarios Scenario 2 Scenario 1 Be is produced in the He shell before the passage of shock. Sensitive to explosion energy. Be survives for low explosion energy accompanied by fallback. Happens via neutron capture in low metallicity progenitors. Generally needs inverted mass hierarchy with a hard spectra to produce enough neutrons. Can also work for soft spectra and in scenarios without oscillation. Also the site for cold r-process in the He shell. Be is produced in the He shell after passage of shock. Not very sensitive to explosion energy and all of the ejecta comes out. Has nothing to do with neutron capture. Can happen at metallicities (potentially). 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. No associated r-process.

8. 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.

9. Non-GCR Sources for Bulk Be Production Neutron Star Mergers? Goriely, Bauswein & Janka (2011)

10. 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.