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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 Problems and challenges Massive stellar evolution Roni Waldman
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
First: Overview of a massive star evolution sequence CCSN progenitor M=15M Massive stellar evolution Roni Waldman
M=15M Zero age main sequence Time step
M=15M Main sequence Time step
M=15M Main sequence Time step
M=15M End of main sequence Time step
M=15M Shell H burning Time step
M=15M Shell H burning Time step
M=15M Core He ignition Time step
M=15M Core He burning Time step
M=15MCore He burning – max C abundance Time step
M=15M Core He exhausted Time step
M=15M Shell He burning Time step
M=15M Core C ignition Time step
M=15M Core C exhausted Time step
M=15M Shell C burning Time step
M=15M Core Ne burning Time step
M=15M Shell Ne burning Time step
M=15M Core O burning Time step
M=15M Shell O burning Time step
M=15M Core Si ignites Time step
M=15M Core Si burning Time step
M=15MSi exhausted Fe core collapse Time step
M=15MNicer view of burning shells C Si O Woosley et al 2002 Massive stellar evolution Roni Waldman
Going to lower mass end AGB star 5 M Massive stellar evolution Roni Waldman
M=5M AGB star log10(t-tend/yr) Massive stellar evolution Roni Waldman
Close up on the double shell H burning He burning log10(t-tend/yr) Massive stellar evolution Roni Waldman
A more detailed view 2 Msun Massive stellar evolution Roni Waldman
M=9Msun TP-AGB Siess 2010 Massive stellar evolution Roni Waldman
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
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
Intermediate region Super AGB star 8 M Massive stellar evolution Roni Waldman
M=8Msun SAGB starCarbon ignites off-center log10(t-tend/yr) Massive stellar evolution Roni Waldman
M=8MsunClose up on off-center C burning Massive stellar evolution Roni Waldman
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
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
Final fate in the intermediate zone Langer 2012 Massive stellar evolution Roni Waldman
Massive stellar evolution What can we compare to? Massive stellar evolution Roni Waldman
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
Comparison of HR diagram Ekstrom et al 2012 Massive stellar evolution Roni Waldman
Uncertainties • Mass loss • Convection • Reaction rates • Opacities Massive stellar evolution Roni Waldman
Mass loss Massive stellar evolution Roni Waldman
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
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
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
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
Convection Uncertainties Massive stellar evolution Roni Waldman
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