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Massive stellar evolution. Problems and challenges. Problems in modeling massive star evolution. Modeling is mostly done in the 1D approximation.  Considerable uncertainties: mass loss, convection and mixing. New additions to models: rotation, magnetic fields, 3D convection.

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Massive stellar evolution


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    1. Massive stellar evolution Problems and challenges Massive stellar evolution Roni Waldman

    2. Problems in modeling massive star evolution • Modeling is mostly done in the 1D approximation.  • Considerable uncertainties: mass loss, convection and mixing. • New additions to models: rotation, magnetic fields, 3D convection. • Increasing wealth of observational data enable better constraints on models. Massive stellar evolution Roni Waldman

    3. First: Overview of a massive star evolution sequence CCSN progenitor M=15M Massive stellar evolution Roni Waldman

    4. M=15M Zero age main sequence Time step

    5. M=15M Main sequence Time step

    6. M=15M Main sequence Time step

    7. M=15M Main sequenceConvection starts receding Time step

    8. M=15M End of main sequence Time step

    9. M=15M Shell H burning Time step

    10. M=15M Shell H burning Time step

    11. M=15M Core He ignition Time step

    12. M=15M Core He burning Time step

    13. M=15MCore He burning – max C abundance Time step

    14. M=15M Core He exhausted Time step

    15. M=15M Shell He burning Time step

    16. M=15M Core C ignition Time step

    17. M=15M Core C exhausted Time step

    18. M=15M Shell C burning Time step

    19. M=15M Core Ne burning Time step

    20. M=15M Shell Ne burning Time step

    21. M=15M Core O burning Time step

    22. M=15M Shell O burning Time step

    23. M=15M Core Si ignites Time step

    24. M=15M Core Si burning Time step

    25. M=15MSi exhausted  Fe core collapse Time step

    26. M=15MNicer view of burning shells C Si O Woosley et al 2002 Massive stellar evolution Roni Waldman

    27. Going to lower mass end AGB star 5 M Massive stellar evolution Roni Waldman

    28. M=5M AGB star log10(t-tend/yr) Massive stellar evolution Roni Waldman

    29. Close up on the double shell H burning He burning log10(t-tend/yr) Massive stellar evolution Roni Waldman

    30. A more detailed view 2 Msun Massive stellar evolution Roni Waldman

    31. M=9Msun TP-AGB Siess 2010 Massive stellar evolution Roni Waldman

    32. AGB star • If no mass loss  C will eventually ignite! • Growth of core is overcome by mass loss. • End in CO white dwarfs • This is sensitive to: • Metallicity • Uncertainty in mass loss Massive stellar evolution Roni Waldman

    33. Problems arise • Observation of luminosity function of C-stars show that stellar evolution calculations do not predict sufficiently large dredge-up at sufficiently low core mass. • Mixing length parameter, calibrated from solar data, is inadequate. • Or, mixing length theory is altogether inadequate. • 3D modeling of convection is needed! Massive stellar evolution Roni Waldman

    34. Intermediate region Super AGB star 8 M Massive stellar evolution Roni Waldman

    35. M=8Msun SAGB starCarbon ignites off-center log10(t-tend/yr) Massive stellar evolution Roni Waldman

    36. M=8MsunClose up on off-center C burning Massive stellar evolution Roni Waldman

    37. Massive star evolutionOutcomes Does carbon ignite? Yes No Does neon ignite? AGB No Yes SAGB CO WD Does Ne core grow to Chandrasekhar mass? Continue burning oxygen, silicon No CCSN Yes ONe WD ECSN Massive stellar evolution Roni Waldman

    38. Final fate of stars:Different codes Max He core before 2nd dredge-up Ledoux + slow semiconvection Schwartzschild Ledoux + fast semiconvection Ledoux + medium semiconvection MESA Iron core collapse SN Max He core after 2nd dredge-up SAGB ONe WD or ECSN AGB CO WD Adapted from Poelarends et al. 2008 Massive stellar evolution Roni Waldman

    39. Final fate in the intermediate zone Langer 2012 Massive stellar evolution Roni Waldman

    40. Massive stellar evolution What can we compare to? Massive stellar evolution Roni Waldman

    41. Observables • Characteristics of the Sun • Width of the MS band in the HRD • The positions of red giants and red supergiants (RSG) in the HRD • Ratio of WR to O stars • Surface composition changes • Averaged rotational surface velocities Massive stellar evolution Roni Waldman

    42. Comparison of HR diagram Ekstrom et al 2012 Massive stellar evolution Roni Waldman

    43. Uncertainties • Mass loss • Convection • Reaction rates • Opacities Massive stellar evolution Roni Waldman

    44. Mass loss Massive stellar evolution Roni Waldman

    45. What is mass loss • Hot stars – momentum transferred from radiation to matter through absorption by metal lines • Cool stars also have: • Absorption by dust • Pulsations • Examples: • De Jager 88 empirical fit: • Vink 2001 hot star models: Massive stellar evolution Roni Waldman

    46. How well do we know the mass loss rates? Comparison of various mass loss rate prescriptions for RSG stars (Mauron & Josselin 2011) Massive stellar evolution Roni Waldman

    47. Mass lossHow good can an empirical fit be? • Sample stars adjacent in HR diagram have more than order of magnitude difference in mass loss! • Fit formula accuracy: • ~2 for hot luminous stars • ~5 for cool luminous stars • Episodic mass loss • Need for modeling! • Currently available for hot stars only. 5.2 6.9 de Jager et al 1988 Massive stellar evolution Roni Waldman

    48. Implications of uncertainty in mass loss • Uncertainty in mass loss has considerable effect on final masses and residual H • This determines which stars will become type IIP SNe SN IIP Massive stellar evolution Roni Waldman

    49. Convection Uncertainties Massive stellar evolution Roni Waldman

    50. Uncertainties in Convection • Convection is treated by 1D MLT model, with single parameter – calibrated from solar model. • Is that universal? • Modeling of SN IIP light curves suggests radii too high mixing length parameter too low. Massive stellar evolution Roni Waldman