Reminders

1 Online Quiz Chapter 12 Due Today2 Online Quiz Chapter 13 Due Next Week3 Read Chapters 12-13

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Lecture 23 — Helium Flash, LowMass Evolution, Close Binary

Evolution, Type Ia Supernovae,Massive Star Evolution

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Turnoff In HR Diagram DeterminesAge

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Helium Burning

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Result of Helium Burning is bothCarbon and Oxygen

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Pressure-Temperature Thermostat

Ordinary Pressure P ∝ ρTIf T rises, P rises, star expands, T fallsWith Quantum Mechanical Pressure P ∝ ργ

If T rises, P stays constant, nuclear reactionrates get bigger, T rises more, nuclearreaction rates get bigger, BOOM!!!!!

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Quantum Mechanical Pressure: TheHelium Flash

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Clicker Question

The property of a star that determines itsdestiny is its:

(a) density(b) radius(c) luminosity(d) mass

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Stellar Evolution of Low andIntermediate Mass Stars I

Exhaust Hydrogen in CoreLeave the MSIgnite Hydrogen in ShellForm Red GiantBegin Helium Burning in Core (low massstars have helium flash)

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Stellar Evolution of Low andIntermediate Mass Stars II

Now on Horizontal Branch or Helium MainSequenceExhaust Helium in Core, leaving Carbon +Oxygen CoreIgnite Helium in ShellAscend the Asymptotic Giant Branch (AGB)Lose Most of their Mass as Planetary NebulaEnd up as C+O White Dwarf

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Globulars Old: Few Metals

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Evolution of a 3 M� Star

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Evolution of the Sun

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Evolution in HR Diagram

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Ring Nebula

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Energy Transport is Different inMassive Stars

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Carbon burningOnly in Massive Stars M ∼> 8 M�

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Clicker Question

On the main sequence the Sun uses:(a) CNO cycle(b) p-p cycle(c) triple alpha process(d) gravitational contraction

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Clicker Question

On the main sequence a 3 M� star uses:(a) CNO cycle(b) p-p cycle(c) triple alpha process(d) gravitational contraction

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Close Binary Evolution: RocheLobes

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Close Binary Evolution: MassTransfer

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