Massive Binariesand self enrichment of globular clusters

Norbert Langer (Bonn)Onno Pols (Utrecht)

Rob Izzard (Brussels)

Selma de MinkUtrecht Bonn STScI (Nov 2010)

A&A 507, 1 (2009)Archiv: 0910.1086

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Introduction

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Multiple populations that differ in

composition and possibly in age

Globular clusters… not so simple as we thought they were

• Stellar abundancese.g. Cohen+78, Gratton+04, Carretta+09ab

• Color magnitude diagramse.g. Bedin+04, D’Antona+05, Piotto+07

Stellar rotation natural explanation some features of intermediate-age clusters?

Bastian & De Mink (2009)

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Simplified formation scenario

1. Initial cloud with “normal” composition

2. Formation of the first generation of stars

6. The multiple populations we see today.

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Simplified formation scenario

1. Initial cloud with “normal” composition

2. Formation of the first generation of stars

3. “Massive ”stars eject pro-cessed material

4. Polluting the cluster

5. Forming a second generation.

6. The multiple populations we see today.

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The polluters?Requirements ejecta

I. Low velocity to remain within the potential well of the cluster

II. Processed by H-burning at high temperature

e.g. Prantzos+07

Challenges• Composition

• Amount

e.g. Gratton+04, D’Antona+Caloi08

Proposed sourcesI. Massive AGB stars:

e.g. Cottrell+DaCosta+81, Ventura+01

II. Spin stars:fast rotating massive stars

e.g. Decresin+07

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Mass budget

Kroupa 2001

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Mass budget

Ciotti+91, D’Ercole+08 Prantzos+Charbonnel06,

Decressin+07

Assuming all stars rotate

fast!(>0.8 break-up)

Assuming all 4-9 Msun stars ar single and contribute

Anomalous IMF ?Strong preferential loss of normal

stars ?External pollution ?

Alterative source?

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Massive binariesstars are also ...

... not as simple as we thought they were

hoped

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- The most massive star enriches its inner layers with products of proton capture reactions.

Interacting Binaries

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- The most massive star enriches its inner layers with products of proton capture reactions.

Interacting Binaries

He core“Strongly” processed

“Mildly” processed

UnprocessedC↓N

↑

O↓Na↑

Mg↓Al↑

Li↓

De Mink et al. (2009a)

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- The most massive star enriches its inner layers with products of proton capture reactions.

- When it expands beyond a critical radius, it is stripped from its entire envelope.

- The first non-enriched layers are accreted by the companion.

Interacting Binaries

Unprocessed

De Mink et al. (2009a)

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- The most massive star enriches its inner layers with products of proton capture reactions.

- When its expands beyond a critical radius, the is stripped from its entire envelope.

- The first non-enriched layers are accreted by the companion.

- Processed material is shedded from the system at low velocity.

Interacting Binaries

Strongly processed

Mildly processed

Unprocessed

De Mink et al. (2009a)

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I. Post-interaction: common envelope ejection Cataclysmic variables, X-ray binaries, double white dwarfs, double

neutron stars, Planetary nebulae with binary cores

II. Interacting binaries Algol type systems Tests from eclipsing binaries

Observational Evidence

Refsdal+74, Sarna93, deGreve+Linnell94, Figueiredo+94, vanRensbergen+06

e.g. Iben+Livio93

De Mink, Pols, Hilditch (2007)

“Show case”: Massive interacting binary: RY Scuti• Circum-binary disk (1AU), Nebula (2000 AU)• Rich in He, N, Poor in O, C• Velocity 30-70 km/s• Dust and clumps

Gehrz+01, Smith+01,02,

Grundstrom+07

Evidence for mass loss from binaries - comes from a wide variety of observed systems and- seems to be a common phenomenon.

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• 3D Hydro simulations

• Evolutionary calculations- Expansion -> contact- Spin up

Mass ejection from binaries – models

Ultich+Burger76, Flannery+Ulrich77Packet81, Barai+04, Petrovic+05

With courtesy of D. Bisikalo

e.g. Nazarenko+Glazunova06, Zhilkin+Bisikalo09

Utrecht/Bonn binary stellar evolution code Stellar evolution, mass loss, Extensive nucleosynthetic network, Mass

and angular momentum transfer, Effects of tides, Effects of rotationDe Mink, et al. 2009b,

Yoon+06, Petrovic+05, Heger+00, Langer

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Typical massive binary system: 20 Msun star with a 15 Msun comp. in a 12 days orbit (Case B)

Primary star loses 12 Msun

- 1.5 Msun is accreted- 10.5 Msun is ejected

Ejecta are - enriched in He, N, Na, Al- depleted in C, O, (Mg)

Example detailed model

Ejected mass (Msun)

Rela

tive

surfa

ce

abun

danc

e

Ejected mass (Msun)

De Mink et al. (2009a)

Mass ejected slowly (Msun)Binary 10.5Spin star 1.7

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Additional remarks

Evolution was followed until end of the evolution of the primary, but the secondary can still pollute the cluster

• as a spin star• by reverse mass transfer

We assumed slow initial rotation. Fast rotation would induce extra mixing and could pollute an even larger fraction of the envelope

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Mass Budget

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Currently not very high (among the low mass stars!)

What about the massive stars?• close binary fraction > 50%

in nearby OB associations + open clusters

• Even higher in dense cores of globular clusters?- Initial/quick Mass segregation- Early core collapse- Dynamical interactions of stars and gas (dissipative!)- …

Binary fraction

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Binaries as sources of enrichment

Without commonly made assumptions

• Normal IMF• No a very high fraction of very fast rotators• No external pollution• No extreme preferential loss of 1st generation stars

De Mink et al. (2009a)

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Massive Binaries:

Assuming that the complete envelope is processed and returned and that all stars above 10 Msun are in interacting binaries

Binaries as sources of enrichmentDe Mink et al. (2009a)

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Massive Binaries:

Assuming that the complete envelope is processed and returned and that all stars above 10 Msun are in interacting binaries

Binaries as sources of enrichmentDe Mink et al. (2009a)

Binaries can return more processed mass than AGB and spin stars together.

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Intermediate mass binaries:

Lower mass stars may also provide processed material showing some of the anticorrellations produced at lower T.

Massive Binaries:

Assuming that the complete envelope is processed and returned and that all stars above 10 Msun are in interacting binaries

Binaries can return more processed mass than AGB and spin stars together.

Binaries as sources of enrichmentDe Mink et al. (2009a)

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Conclusion

• Interactions between massive stars and therefore mass stripping are likely in center of massive young clusters

• Interacting stars can eject material - processed by H-burning- at low velocities- in large amounts

• Possibly more important than the previously suggested sources (at least in terms of ejecta mass)

• Relieve of the need for extreme additional assumptions- a top heavy IMF- extreme polution or preferenial mass loss

Conclusion Interacting stars are promising sources for self enrichment of globular clusters

A&A 507, 1 (2009)Archiv: 0910.1086

S.E. de Mink S. E. de Mink

A&A 507, 1 (2009)Archiv: 0910.1086