AGB stars as laboratories for nuclear physics
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1 AGB stars as laboratories for nuclear physics John Lattanzio with Amanda Karakas 1, Lisa Elliott, Simon Campbell, Maria Lugaro 2, Carolyn Doherty Centre for Stellar and Planetary Astrophysics, Monash University,Australia 1 now at Centre for Computational Astrophysics, St Marys University, Halifax 2 now at Institute of Astronomy, Cambridge University
2
3 AGB Nucleosynthesis 1. He Flashes and hot bottoms etc 2. C stars 3. S-process elements F 25 Mg and 26 Mg (and Al isotopes) 23 Na 7 Li 14 N 9. etc
4 HR Diagram (Globular Cluster) AGB (Second giant branch) Horizontal Branch (core He burning) RGB (first giant branch) Blue Stragglers Main sequence (H burning) White Dwarfs
5 HR Diagram (Globular Cluster) Here be monsters Giants complicated! Friendly Main Sequence Stars Graveyard
6 Nucleosynthesis
7 Z = number of protons Chart of the Nuclides: The big boys/girls periodic table N = number of neutrons
8 Why was it OK to have H, He and Z? For the structure we need the energy generation Burning H to He or He to C covers most of HRD! So we can make accurate models with only H and He burning Very few species needed Me: H, He 3, He 4, C 12, N 14 and O 16
9 H burning PP chains or CNO cycle(s) PP chains: pure H gas is all that s needed CNO cycles require CNO as catalysts
10 First reaction: p + p D 2 + γ D 2 + p He 3 + γ He 3 + He 3 He 4 + 2p PP Chains
11 Branching reaction: PP Chains He 3 + He 4 Be 7 + γ Be 7 + p B 8 He 4 + He 4 Be7 + e Li 7 Li 7 + p He 4 + He 4
12 CNO Cycles: First step is CN cycle C p C 12 + He 4
13 CNO Cycles
14 And then things went CRAZY!
15 Who were the trouble makers? Pre-solar meteorite grains Pieces of stars! In the lab!
16 The Nuclear Network we now use 74 species 506 reactions
17 Basic Stellar Evolution: Mass is the key! no Die as a Brown Dwarf Burn H? yes Die as a He White Dwarf no Burn He? yes no Die as a CO White Dwarf Burn C? yes Die as a O-Ne-Mg White Dwarf no More burning? yes Wolf-Rayet SN II
18 Basic Stellar Evolution: Mass is the key! Mass Initial Mass Function: N ~ M -2.3 SN & WR AGB stars Don t burn more O-Ne-Mg WD Burn more Don t burn C C-O White Dwarf Burn C Don t burn He He White Dwarf Burn He Don t burn H Brown Dwarf Burn H
19 Basic Stellar Evolution at M=1 and 5 Basic Evolution: M=1 & 5
20 H burning summary at M=1
21 End of H burning: He ignition
22 Following He exhaustion: AGB Evolution
23 Early AGB Evolution: Second Dredge-Up
24 Thermally pulsing AGB phase Deep convective Envelope Thin radiative zone H-burning shell He-rich intershell He-burning shell CO core
25 AGB Evolution
26 AGB evolution: M = 6.5, Z=0.02
27 AGB Evolution Energy Sources
28 AGB Evolution Shell Movement
29 Dredge-Up Parameter: λ
30 AGB Evolution Mixing Zones
31 Anatomy of a Thermal Pulse He - C 14 N to 22 Ne M>3: 22 Ne to 25 Mg and 26 Mg
32 AGB movies
33 M MS S C(N) Add C at each drede-up episode Eventually C/O > 1 M star turns into a C star Fits observations (pretty much )
34 Neutron capture: the s and r β + decay: p n + ν + β + processes Valley of beta stability β - decay: n p + ν + β -
35 S-process elements in AGB stars Neutron capture on Fe: Sr, Y, Zr, Ba, Kr etc
36 Mg isotopes in field stars Gay and Lambert found some enhancements in heavy isotopes Does not fit SN models
37 Anatomy of a Thermal Pulse He - C 14 N to 22 Ne M>3: 22 Ne to 25 Mg and 26 Mg
38 Mg 25,26 (and maybe Al 26,27) For T > 300 million (M > 2.5) Al 26 and Al 27 dredged to surface Mg 25 and Mg 26 dredged to surface Another source of neutrons! Ne 22 (α,n)mg 25 Ne 22 (α,γ ) Mg 26 Al 26 and Al 27 made by H shell via proton captures on Mg Al engulfed by convection
39 Intershell abundances: as a function of mass & Z
40 Evolution of the Mg isotopes
41 Massive stars produce most of the galactic magnesium, which is primarily 24 Mg at low Z But 3-6 M sun AGB stars can produce large amounts of the heavy magnesium isotopes (Y. Fenner, A. Karakas, B. Gibson, J. Lattanzio)
42 AGB stars are needed to recover the observed 25,26 M/ 24 Mg ratios at low metallicity Limongi et al. (2002) calculations generate more 25,26 Mg than Woosley & Weaver (1995) (Y. Fenner, A. Karakas, B. Gibson, J. Lattanzio, PASA, 2003)
43 Fluorine Observations show [F/O] correlates with C/O This implicates thermal pulses Complicated - different reaction paths - depends on mass - depends on composition - depends on pulse number
44 Fluorine
45 3. And finally N 15 (α,γ)f Protons made here by Al 26 (n,p)mg O 18 (p,α)n Protons made here by N 14 (n,p)c 14
46 GCE of 19 F Renda et al (submitted) SN, WR and AGB SN & WR x = Milky Way = LMC = ω Cen SN only
47 Sodium 12 C 14 N 22 Ne 23 Na 23 Na 22 Ne 23 Na Note: some 23 Na is primary and some is secondary!
48 Making Li
49 Making Li
50 Primary Nitrogen in the early Universe Various observations 9eg Lyman alpha clouds) show a primary source of N in the early Universe AGB stars again? Primary C is produced by dredge-up (H He C) CNO cycles make N 14 from C and O Thus HBB makes Primary N 14
51
52 Summary of Nucleosynthesis in AGB stars Dredge-up increases: C, Ne 22, Mg 25, Mg 26 H shell and HBB (M>4) burns: 1) C and O into N: O down and N up 2) Ne22 into Na23: Na up 3) Mg25 and Mg26 made: Mg 25,26 increased More massive stars (M > 6?): 1) Mg24 burned into Al27: Mg 24 down Al 27 up Overall 1) Increases in N, Na, heavy Mg, Al 2) Decreases in O, Mg 24
53 The End?
54 More appropriate for a theorist Play Tom Lehrer Song
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