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Nucleosynthesis in R Coronae Borealis Stars
Richard Longland
Universitat Politècnica de CatalunyaGrup 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
Don’t look up!
R Coronae Borealis (HIP 77442)I Peculiarities discovered in 1795I “Reverse Nova”I Fades periodically to magnitude 14
I Yellow supergiant starsI Sudden fading episodes up
to 9 magnitudesI No atmospheric hydrogen
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 3 / 12
Don’t look up!
R Coronae Borealis (HIP 77442)I Peculiarities discovered in 1795I “Reverse Nova”I Fades periodically to magnitude 14
I Yellow supergiant starsI Sudden fading episodes up
to 9 magnitudesI No atmospheric hydrogen
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 3 / 12
R CrB stars
To explain:Hydrogen deficiencyC, N, O, Ne, F, Li (andothers) enrichment[X] = log(X/X�)12C/13C> 500No known R CrB binary
Final-FlashI Dying AGB starI Final, strong, helium-shell flashI Remaining envelope blown awayI Inner-regions revealed
Double DegenerateI CO + He white dwarfs mergeI He white dwarf disrupted and accretedI Helium burning commences, accreted
material expands
Jeffery, S et al. MNRAS 414 (2011) 3599Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 4 / 12
R CrB stars
To explain:Hydrogen deficiencyC, N, O, Ne, F, Li (andothers) enrichment[X] = log(X/X�)12C/13C> 500No known R CrB binary
Final-FlashI Dying AGB starI Final, strong, helium-shell flashI Remaining envelope blown awayI Inner-regions revealed
Double DegenerateI CO + He white dwarfs mergeI He white dwarf disrupted and accretedI Helium burning commences, accreted
material expands
Jeffery, S et al. MNRAS 414 (2011) 3599Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 4 / 12
Making a white dwarf system
Binary system of main sequencestars
More massive star expands andloses envelope CommonEnvelope StageStar exposes core (white dwarf)Second star undergoes similarevolutionLoses envelopeBinary white dwarf systemremains
White dwarfs lose angularmomentum through gravitationalwave emissionMerging event!
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12
Making a white dwarf system
Binary system of main sequencestarsMore massive star expands andloses envelope CommonEnvelope Stage
Star exposes core (white dwarf)Second star undergoes similarevolutionLoses envelopeBinary white dwarf systemremains
White dwarfs lose angularmomentum through gravitationalwave emissionMerging event!
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12
Making a white dwarf system
Binary system of main sequencestarsMore massive star expands andloses envelope CommonEnvelope StageStar exposes core (white dwarf)
Second star undergoes similarevolutionLoses envelopeBinary white dwarf systemremains
White dwarfs lose angularmomentum through gravitationalwave emissionMerging event!
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12
Making a white dwarf system
Binary system of main sequencestarsMore massive star expands andloses envelope CommonEnvelope StageStar exposes core (white dwarf)Second star undergoes similarevolutionLoses envelope
Binary white dwarf systemremains
White dwarfs lose angularmomentum through gravitationalwave emissionMerging event!
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12
Making a white dwarf system
Binary system of main sequencestarsMore massive star expands andloses envelope CommonEnvelope StageStar exposes core (white dwarf)Second star undergoes similarevolutionLoses envelopeBinary white dwarf systemremains
White dwarfs lose angularmomentum through gravitationalwave emission
Merging event!
3.5M� + 2.0M� → CO + He
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12
Making a white dwarf system
Binary system of main sequencestarsMore massive star expands andloses envelope CommonEnvelope StageStar exposes core (white dwarf)Second star undergoes similarevolutionLoses envelopeBinary white dwarf systemremains
White dwarfs lose angularmomentum through gravitationalwave emissionMerging event!
3.5M� + 2.0M� → CO + He
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 5 / 12
White Dwarf Compositions
The detailed compositions of the two white dwarfs must be carefullyconsideredSimply assuming pure CO and He is too simplistic
Renedo, I. et al., ApJ 717 (2010) 183
Not all atmosphericmaterial will be lost inmass loss stageSmall “buffers” of materialwill remainThese buffers areessential in understandingobservational signaturesof white dwarf mergersSPH tracer particleabundances obtainedfrom these models
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 6 / 12
Understanding Lithium - 3He Production
Thin hydrogen buffer:
p + p→d
d + p→3He3He +3 He→4He + 2p
3He reaches an equilibrium in theH-buffer
(3He)e =1
2〈σv〉33
[−(4He)〈σv〉34 +
√2(H)2〈σv〉pp〈σv〉33 + (4He)2〈σv〉234
]
Centre of hydrogen buffer(4He) = (H) = 0.5(3He)e ≈ 10−5
Equilibrium reached in 105 yearsMass of hydrogen buffer ≈ 10−3M�
Higher 3He abundance inouter regionsServes only to increase3He in buffer underconvective processes
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 7 / 12
Understanding Lithium - 3He Production
Thin hydrogen buffer:
p + p→d
d + p→3He3He +3 He→4He + 2p
3He reaches an equilibrium in theH-buffer
(3He)e =1
2〈σv〉33
[−(4He)〈σv〉34 +
√2(H)2〈σv〉pp〈σv〉33 + (4He)2〈σv〉234
]
Centre of hydrogen buffer(4He) = (H) = 0.5(3He)e ≈ 10−5
Equilibrium reached in 105 yearsMass of hydrogen buffer ≈ 10−3M�
Higher 3He abundance inouter regionsServes only to increase3He in buffer underconvective processes
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 7 / 12
Understanding Lithium - Lithium Production
During merger, conditions allow3He to fuse with 4He
3He +4 He→7 Be
7Be can decay (EC) into 7Li
BUT! 7Be can also be destroyed
7Be + p −→ 8B7Be + p←→ 8B
8B + p −→ 9C7Be + α −→11C
How does this look with full SPHmodels?
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 8 / 12
Understanding Lithium - Lithium Production
During merger, conditions allow3He to fuse with 4He
3He +4 He→7 Be
7Be can decay (EC) into 7LiBUT! 7Be can also be destroyed
7Be + p −→ 8B7Be + p←→ 8B
8B + p −→ 9C7Be + α −→11C
How does this look with full SPHmodels?
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 8 / 12
Understanding Lithium - Lithium Production
During merger, conditions allow3He to fuse with 4He
3He +4 He→7 Be
7Be can decay (EC) into 7LiBUT! 7Be can also be destroyed
7Be + p −→ 8B7Be + p←→ 8B
8B + p −→ 9C7Be + α −→11C
How does this look with full SPHmodels?
−4
−2
0
2
1e+08 3e+08 5e+08 7e+08
10
20
30
40
50
−4
−4
−4
−4−2
0
2
Max Temp (K)
Fall
Tim
e(s
)
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 8 / 12
Hydrodynamic Merger Nucleosynthesis
Using detailed initial abundances, howdoes nucleosynthesis proceed?
Smoothed Particle Hydrodynamics(SPH) models used to model mergingof two white dwarfs
I Stars represented by 300 000particles
Each particle contains thelocal temperature and densityLimited nuclear network usedto track energyPostprocessing of tracerparticles possible withextended nuclear network
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 9 / 12
Hydrodynamic Merger Nucleosynthesis
Using detailed initial abundances, howdoes nucleosynthesis proceed?Smoothed Particle Hydrodynamics(SPH) models used to model mergingof two white dwarfs
I Stars represented by 300 000particles
Each particle contains thelocal temperature and densityLimited nuclear network usedto track energyPostprocessing of tracerparticles possible withextended 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
R CrB results
Longland et al. ApJL 737 (2011) L34
Staff et al. ApJ 757 (2012) 76
Initial abundances read in from whitedwarf models
Consider hot coronaI Very good agreementI Different assumptions of mixing produce
different abundances
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 whitedwarf modelsConsider hot corona
I Very good agreementI Different assumptions of mixing produce
different abundancesRichard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 11 / 12
ConclusionsModels of merging white dwarfs has been successful in explaining theorigin of R CrB starsDetailed nucleosynthesis models are only just beginningUnderstanding the prior evolution of white dwarfs is essential to modellingthese 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
What are the possibilities?
First calculations made in late 1980’sIben & Tutukov, ApJ 311 (1986) 311Nelemans, G., et al., A&A 365 (2001) 491
Half of all star systems are binary systems2× 108 WD+WD systems in our galaxyHalf of these will mergeSome possibilities:
Mass 1 Mass 2 Final Binary Percentage1.4 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 heliumwhite dwarfs?
I Common envelope stage occurs whenstar is red giant
I Mass lost before helium burning beginsI Gravitational energy no longer enough for
3α →12 C
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 14 / 12
What are the possibilities?
First calculations made in late 1980’sIben & Tutukov, ApJ 311 (1986) 311Nelemans, G., et al., A&A 365 (2001) 491
Half of all star systems are binary systems2× 108 WD+WD systems in our galaxyHalf of these will mergeSome possibilities:
Mass 1 Mass 2 Final Binary Percentage1.4 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 heliumwhite dwarfs?
I Common envelope stage occurs whenstar is red giant
I Mass lost before helium burning beginsI Gravitational energy no longer enough for
3α →12 C
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 14 / 12
What are the possibilities?
First calculations made in late 1980’sIben & Tutukov, ApJ 311 (1986) 311Nelemans, G., et al., A&A 365 (2001) 491
Half of all star systems are binary systems2× 108 WD+WD systems in our galaxyHalf of these will mergeSome possibilities:
Mass 1 Mass 2 Final Binary Percentage1.4 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 heliumwhite dwarfs?
I Common envelope stage occurs whenstar is red giant
I Mass lost before helium burning beginsI 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� modelIdentify escaping particlesexceeding their escape velocities184 escaping particles withM = 4.9× 10−4M�
Limitations of modelI Limited solar evolution models -
need to be supplemented byscaled solar abundances
I Low resolution (only 300 000particles)
I Escape particle averagingDo we treat every particle as agrain? Or use averaging?
I Do the particles condense intograins?!
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 16 / 12
Nitrogen and Carbon
Clayton and Nittler,Annu. Rev. Astron. Astrophys. 42 (2004) 39–78
Consider nitrogen andcarbon2D abundancehistogramSolar abundances:
I High 14N/15NI Low 12C/13C
Low metalicity models(z = 1× 10−5)
I More spread innitrogen and carbon
I Particles resembleA & B grains
I Consistent withborn-again AGBstars
Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 17 / 12
Nitrogen and Carbon
Clayton and Nittler,Annu. Rev. Astron. Astrophys. 42 (2004) 39–78
Consider nitrogen andcarbon2D abundancehistogramSolar abundances:
I High 14N/15NI Low 12C/13C
Low metalicity models(z = 1× 10−5)
I More spread innitrogen and carbon
I Particles resembleA & B grains
I Consistent withborn-again AGBstars
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
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