Nucleosynthesis in R Coronae Borealis Stars Richard Longland Universitat Politècnica de Catalunya Grup d’Astronomia i Astrofísica June 13th, 2013 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 1 / 12 Outline 1 Introduction 2 Prior Evolution Nucleosynthesis 3 Merger Nucleosynthesis 4 Conclusions Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 2 / 12 R Coronae Borealis (HIP 77442) I Yellow supergiant stars I Sudden fading episodes up I Peculiarities discovered in 1795 to 9 magnitudes I “Reverse Nova” I No atmospheric hydrogen I Fades periodically to magnitude 14 Don’t look up! Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 3 / 12 Don’t look up! R Coronae Borealis (HIP 77442) I Yellow supergiant stars I Sudden fading episodes up I Peculiarities discovered in 1795 to 9 magnitudes I “Reverse Nova” I No atmospheric hydrogen I Fades periodically to magnitude 14 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 3 / 12 Final-Flash I Dying AGB star I Final, strong, helium-shell flash I Remaining envelope blown away I Inner-regions revealed Double Degenerate I CO + He white dwarfs merge I He white dwarf disrupted and accreted I Helium burning commences, accreted material expands R CrB stars To explain: Hydrogen deficiency C, N, O, Ne, F, Li (and others) enrichment [X] = log(X=X ) 12C/13C> 500 No known R CrB binary Jeffery, S et al. MNRAS 414 (2011) 3599 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 4 / 12 R CrB stars To explain: Hydrogen deficiency C, N, O, Ne, F, Li (and others) enrichment [X] = log(X=X ) 12C/13C> 500 No known R CrB binary Final-Flash I Dying AGB star I Final, strong, helium-shell flash I Remaining envelope blown away I Inner-regions revealed Double Degenerate I CO + He white dwarfs merge I He white dwarf disrupted and accreted I Helium burning commences, accreted material expands Jeffery, S et al. MNRAS 414 (2011) 3599 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 4 / 12 More massive star expands and loses envelope Common Envelope Stage Star exposes core (white dwarf) Second star undergoes similar evolution Loses envelope Binary white dwarf system remains White dwarfs lose angular momentum through gravitational wave emission Merging event! Making a white dwarf system Binary system of main sequence stars Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12 Star exposes core (white dwarf) Second star undergoes similar evolution Loses envelope Binary white dwarf system remains White dwarfs lose angular momentum through gravitational wave emission Merging event! Making a white dwarf system Binary system of main sequence stars More massive star expands and loses envelope Common Envelope Stage Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12 Second star undergoes similar evolution Loses envelope Binary white dwarf system remains White dwarfs lose angular momentum through gravitational wave emission Merging event! Making a white dwarf system Binary system of main sequence stars More massive star expands and loses envelope Common Envelope Stage Star exposes core (white dwarf) Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12 Binary white dwarf system remains White dwarfs lose angular momentum through gravitational wave emission Merging event! Making a white dwarf system Binary system of main sequence stars More massive star expands and loses envelope Common Envelope Stage Star exposes core (white dwarf) Second star undergoes similar evolution Loses envelope Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12 Merging event! Making a white dwarf system Binary system of main sequence stars More massive star expands and loses envelope Common Envelope Stage Star exposes core (white dwarf) Second star undergoes similar evolution Loses envelope Binary white dwarf system remains White dwarfs lose angular momentum through gravitational 3:5M + 2:0M ! CO + He wave emission Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12 Making a white dwarf system Binary system of main sequence stars More massive star expands and loses envelope Common Envelope Stage Star exposes core (white dwarf) Second star undergoes similar evolution Loses envelope Binary white dwarf system remains White dwarfs lose angular momentum through gravitational 3:5M + 2:0M ! CO + He wave emission Merging event! Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12 White Dwarf Compositions The detailed compositions of the two white dwarfs must be carefully considered Simply assuming pure CO and He is too simplistic Not all atmospheric material will be lost in mass loss stage Small “buffers” of material will remain These buffers are essential in understanding observational signatures of white dwarf mergers SPH tracer particle abundances obtained from these models Renedo, I. et al., ApJ 717 (2010) 183 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 6 / 12 Centre of hydrogen buffer Higher 3He abundance in (4He) = (H) = 0:5 outer regions 3 −5 ( He)e ≈ 10 Serves only to increase 3 Equilibrium reached in 105 years He in buffer under −3 convective processes Mass of hydrogen buffer ≈ 10 M Understanding Lithium - 3He Production Thin hydrogen buffer: p + p !d d + p !3He 3He +3 He !4He + 2p 3He reaches an equilibrium in the H-buffer q 3 1 4 2 4 2 2 ( He)e = −( He)hσvi34 + 2(H) hσvipphσvi33 + ( He) hσvi34 2hσvi33 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 7 / 12 Understanding Lithium - 3He Production Thin hydrogen buffer: p + p !d d + p !3He 3He +3 He !4He + 2p 3He reaches an equilibrium in the H-buffer q 3 1 4 2 4 2 2 ( He)e = −( He)hσvi34 + 2(H) hσvipphσvi33 + ( He) hσvi34 2hσvi33 Centre of hydrogen buffer Higher 3He abundance in (4He) = (H) = 0:5 outer regions 3 −5 ( He)e ≈ 10 Serves only to increase 3 Equilibrium reached in 105 years He in buffer under −3 convective processes Mass of hydrogen buffer ≈ 10 M Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 7 / 12 BUT! 7Be can also be destroyed 7Be + p −! 8B 7Be + p ! 8B 8B + p −! 9C 7Be + α −!11C How does this look with full SPH models? Understanding Lithium - Lithium Production During merger, conditions allow 3He to fuse with 4He 3He +4 He !7 Be 7Be can decay (EC) into 7Li Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 8 / 12 How does this look with full SPH models? Understanding Lithium - Lithium Production During merger, conditions allow 3He to fuse with 4He 3He +4 He !7 Be 7Be can decay (EC) into 7Li BUT! 7Be can also be destroyed 7Be + p −! 8B 7Be + p ! 8B 8B + p −! 9C 7Be + α −!11C Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 8 / 12 Understanding Lithium - Lithium Production During merger, conditions allow 3He to fuse with 4He 50 3He +4 He !7 Be 2 40 −4 7Be can decay (EC) into 7Li 0 BUT! 7Be can also be destroyed 30 7 8 −4 −2 20 Be + p −! B Fall Time (s) 7 8 Be + p ! B −4 8 9 10 −4 B + p −! C 0 7 11 −2 Be + α −! C 2 −4 1e+08 3e+08 5e+08 7e+08 Max Temp (K) How does this look with full SPH models? Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 8 / 12 Each particle contains the local temperature and density Smoothed Particle Hydrodynamics Limited nuclear network used (SPH) models used to model merging to track energy of two white dwarfs Postprocessing of tracer I Stars represented by 300 000 particles possible with particles extended nuclear network Hydrodynamic Merger Nucleosynthesis Using detailed initial abundances, how does nucleosynthesis proceed? Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 9 / 12 Hydrodynamic Merger Nucleosynthesis Using detailed initial abundances, how Each particle contains the does nucleosynthesis proceed? local temperature and density Smoothed Particle Hydrodynamics Limited nuclear network used (SPH) models used to model merging to track energy of two white dwarfs Postprocessing of tracer I Stars represented by 300 000 particles possible with particles extended nuclear network Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 9 / 12 Lithium Longland et al. A&A 542 (2012) 117 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 10 / 12 Lithium Longland et al. A&A 542 (2012) 117 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 10 / 12 Consider hot corona I Very good agreement I Different assumptions of mixing produce different abundances R CrB results Longland et al. ApJL 737 (2011) L34 Staff et al. ApJ 757 (2012) 76 Initial abundances read in from white dwarf models Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 11 / 12 R CrB results Longland et al. ApJL 737 (2011) L34 Staff et al. ApJ 757 (2012) 76 Initial abundances read in from white dwarf models Consider hot corona I Very good agreement I Different assumptions of mixing produce different abundances Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 11 / 12 Conclusions Models of merging white dwarfs has been successful in explaining the origin of R CrB stars Detailed nucleosynthesis models are only just beginning Understanding the prior evolution of white dwarfs is essential to modelling these events correctly Thanks to EuroGENESIS (and Jordi José)! Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 12 / 12 Backup Slides Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 13 / 12 How do M ≈ 2M stars become helium white dwarfs? I Common envelope stage occurs when star is red giant I Mass lost before helium burning begins I Gravitational energy no longer enough for 3α !12 C What are the possibilities? First calculations