Nucleosynthesis in R Coronae Borealis Stars

Home , R Coronae Borealis

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

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 made in late 1980’s Iben & Tutukov, ApJ 311 (1986) 311 Nelemans, G., et al., A&A 365 (2001) 491 Half of all star systems are binary systems 2 × 108 WD+WD systems in our galaxy Half of these will merge Some possibilities:

Mass 1 Mass 2 Final Binary Percentage 1.4 1.1 He + He (0.31 + 0.32) 53% 3.5 2.0 CO + He (0.61 + 0.35) 14% 4.0 3.0 CO + CO (0.70 + 0.52) 25% 2.2 2.0 He + CO (0.31 + 0.54) 6%

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 14 / 12 What are the possibilities?

Mass 1 Mass 2 Final Binary Percentage 1.4 1.1 He + He (0.31 + 0.32) 53% 3.5 2.0 CO + He (0.61 + 0.35) 14% 4.0 3.0 CO + CO (0.70 + 0.52) 25% 2.2 2.0 He + CO (0.31 + 0.54) 6%

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

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 14 / 12 What are the possibilities?

Mass 1 Mass 2 Final Binary Percentage 1.4 1.1 He + He (0.31 + 0.32) 53% 3.5 2.0 CO + He (0.61 + 0.35) 14% 4.0 3.0 CO + CO (0.70 + 0.52) 25% 2.2 2.0 He + CO (0.31 + 0.54) 6%

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

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 14 / 12 Salt

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 15 / 12 Escaping Particles

0.4 + 0.8 M model Identify escaping particles exceeding their escape velocities 184 escaping particles with −4 M = 4.9 × 10 M Limitations of model

I Limited solar evolution models - need to be supplemented by scaled solar abundances

I Low resolution (only 300 000 particles)

I Escape particle averaging Do we treat every particle as a grain? Or use averaging?

I Do the particles condense into grains?!

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 16 / 12 Low metalicity models (z = 1 × 10−5)

I More spread in nitrogen and carbon

I Particles resemble A & B grains

I Consistent with born-again AGB stars

Nitrogen and Carbon

Consider nitrogen and carbon 2D abundance histogram Solar abundances: 14 15 I High N/ N 12 13 I Low C/ C

Clayton and Nittler, Annu. Rev. Astron. Astrophys. 42 (2004) 39–78

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 17 / 12 Nitrogen and Carbon

Consider nitrogen and carbon 2D abundance histogram Solar abundances: 14 15 I High N/ N 12 13 I Low C/ C Low metalicity models (z = 1 × 10−5)

I More spread in nitrogen and carbon

I Particles resemble A & B grains

I Consistent with born-again AGB stars Clayton and Nittler, Annu. Rev. Astron. Astrophys. 42 (2004) 39–78

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 17 / 12 Silicon

Clayton and Nittler, Annu. Rev. Astron. Astrophys. 42 (2004) 39–78

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 18 / 12 Silicon

Clayton and Nittler, Annu. Rev. Astron. Astrophys. 42 (2004) 39–78

Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 18 / 12