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Mergers in Massive Binaries

Mergers in Massive Binaries. from an evolutionary point of view. Ines Brott (Utrecht), Matteo Cantiello (Utrecht), Joke Claeys (Utrecht) Evert Glebbeek (Hamilton), Adrian Hamers (Utrecht), Rob Izzard (Brussels), Norbert Langer (Bonn), Onno Pols (Utrecht),

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Mergers in Massive Binaries

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  1. Mergers in Massive Binaries from an evolutionary point of view Ines Brott (Utrecht), MatteoCantiello (Utrecht), Joke Claeys (Utrecht) Evert Glebbeek (Hamilton), Adrian Hamers (Utrecht), Rob Izzard (Brussels), Norbert Langer (Bonn), OnnoPols (Utrecht), Sung-Chul Yoon (Bonn) Selma de Mink Utrecht University Lorentz Center Workshop “Stellar Mergers”

  2. Motivation • Massive stars • Cosmic engines, shape the universe • Stellar winds • UV flux • SN explosions • Formation and evolution poorly understood • Very high fraction >50% in close binaries • Mergers from binaries • In contrast to mergers from collisions • Binary mergers dominate in open clusters / loose OB associations • Interaction before merging

  3. Evolutionary point of view Merger Binary evolution before Evolution merger after Which binaries evolve into contact? What is their evolutionary status? What are the main uncertainties? Observational properties, life-time? For clusters: how many “blue stragglers”? Do they end their life, as SNe or GRBs? Mass loss? Mixing?

  4. Outline Initial distributions Evolution into contact 4. Rotationally induced mixing in (near) contact systems 3. Effects of rotationally induced mixing

  5. Initial properties of massive binaries

  6. Binary fraction among massive stars Consistent with fmin = 0.5 Observed binary fraction Courtesy H. Sana

  7. Key parameters • Mass • (Metallicity ) • (Rotation Rate ) • Mass primary • Mass ratio • Orbital period • (Eccentricity) • (Metallicity) • (Rotation rates 2x) Single stars Binary stars

  8. Cumulative distribution functions Data for six open clusters and OB associations ~50 % of the objects is detected a spectroscopic binary Log (Period) Mass Ratio Proceedings paper: Sana et al. 2009

  9. Cumulative distribution functions Data for six open clusters and OB associations ~50 % of the objects is detected a spectroscopic binary Log (Period) Mass Ratio Flat in log P? -> over abundance of systems with P<10 days Flat in q ? For q =0.3-1.0 Proceedings paper: Sana et al. 2009

  10. Summary: initial binary properties • Challenges • Selection effects • Evolutionary effects • Opportunities • VLT-flames Tarantula survey • 1000 Massive stars • Designed to detect binaries

  11. Evolution into contact

  12. Binary evolution • Binary models tell us: • Which binaries come into contact? • When do they come into contact? • What are the properties of both stars at the moment of contact? • Chemical profile • Density / entropy profile Step 1 Step 2

  13. Step 1: Evolution into Roche-lobe overflow

  14. Step 1 • Case A • Porb <5 days • Donor: main sequence star • Case B • Porb = 5 - ~ 500? days • Donor: Hertzsprung gap: H shell burning • Case C • Not important for massive stars (at solar metallicity) • Stellar wind mass loss widens orbit • Massive stars never become giants

  15. Step 2: Evolution into contact Wellstein, Langer, Braun 2001 Log orbital period (d) Mass ratio M2/M1 Z=Z, M1=12M

  16. Step 2: Case A contact • From a grid of ~20.000 binary models computed • for comparison with observed eclipsing binaries De Mink, Pols, Hilditch 2007 Conservative Mass transfer Z=ZSMC, M1=25M

  17. Step 2: Case A contact • From a grid of ~20.000 binary models computed • for comparison with observed eclipsing binaries De Mink, Pols, Hilditch 2007 Non-conservative Mass transfer Z=ZSMC, M1=25M

  18. Uncertainties • Which systems come into contact? • How much mass is accreted/lost form the system • Implementation: when? Associated angular momentum loss? • Entropy accreted material! • How long can the contact configuration last? • Low mass contact systems, W Uma • What evolutionary processes play a role? Mixing? • Does contact imply a merger? • Slow contact : yes

  19. Summary evolution into contact Population synthesis of Case A mergers  Adrian Hamers

  20. Mergers and rotational mixing

  21. Meridional circulation Convective Core Fast rotating stars • Rotational “instabilities” mix rotating massive stars • Eddington-Sweet circulation most efficient process • Mixing process on tKH

  22. Rotational mixing Helium at the surface (mass fraction) Initial Yoon et al 2006

  23. Slow rotator - fast rotator Slow rotator: Standard Evolution Time Fast rotator: Chemically Homogeneous Bifurcation : e.g. Maeder 87, Yoon & Langer 05

  24. RSG WR R~1 Rsun R~1000 Rsun Fast rotator Slow rotator Bifurcation

  25. Yoon, Langer & Norman, 2006

  26. Effects of rotational mixing in (near) contact systems

  27. Binary context Standard Evolution Chemically Homogeneous Time

  28. Z = 10-5M1~100M Single star evolution track

  29. Binary models 1.7 days Roche lobe overflow Z = 10-5M1~M2~100M

  30. Zoom in 1.7 days Z = 10-5M1~M2~100M

  31. Binary models 1.7 days H-shell burning 1.4 days 1.2 days core H-burning Z = 10-5M1~M2~100M

  32. Binary models Start He-burning 1.7 days 1.4 days 1.2 days 1.15 days Core H-burning Z = 10-5M1~M2~100M

  33. Summary

  34. Summary Merger Binary evolution before Evolution merger after

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