Nucleosynthesis in R Coronae Borealis · PDF fileNucleosynthesis in R Coronae Borealis Stars ... of white dwarf mergers ... 117 Richard Longland (UPC) RCrB Nucleosynthesis June 13th,

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


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


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


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!



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




Binary system of main sequencestarsMore massive star expands andloses envelope CommonEnvelope StageStar exposes core (white dwarf)

Second star undergoes similarevolutionLoses envelopeBinary white dwarf systemremains




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




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



Binary system of main sequencestarsMore massive star expands andloses envelope CommonEnvelope StageStar exposes core (white dwarf)Second star undergoes similarevolutionLoses envelopeBinary white dwarf systemremains


3.5M� + 2.0M� → CO + He


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


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


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


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?




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





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


−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

)


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


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


Lithium

Longland et al. A&A 542 (2012) 117


Lithium

Longland et al. A&A 542 (2012) 117


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


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)!


Backup Slides


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









3α →12 C









3α →12 C


Salt


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?!


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


Nitrogen and Carbon


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


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Nucleosynthesis in R Coronae Borealis · PDF fileNucleosynthesis in R Coronae Borealis Stars ... of white dwarf mergers ... 117 Richard Longland (UPC) RCrB Nucleosynthesis June 13th,