astr3 - Stellar Corpses White Dwarfs Planetary Nebula Low...

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Unformatted text preview: Stellar Corpses White Dwarfs Planetary Nebula Low mass stars produce planetary nebula during death throws Also produce white dwarfs 30 km/sec Thermal Pulses During AGB stage Helium shell burning decreases Helium shell collapses and heats up Hydrogen shell above it burns, producing helium Helium from hydrogen-burning shell drops helium into helium shell Helium shell gains mass, shrinks and heats up Helium shell burning occurs in a flash Burning helium shell expands hydrogen shell above it Hydrogen shells density and temperature decreases Hydrogen shell ceases until cycle begins again Electron degeneracy keeps it from collapsing into a black hole Helium shell burning keeps turning on and off, when it turns off it is sudden and a pulse of energy rushes to the surface and blows off Stops when there is no longer any upper atmosphere and there is only a carbon core Planetary Nebula Creation Helium flash significantly increases the luminosity of the AGB star over a small period of time During these flashes, the outer layers are ejected Planetary Nebula Stars .4 to 8 solar masses produce planetary nebula 50,000 planetary nebula in Milky Way expanding shell reaches speeds of 30 km/s cannot observe planetary nebula older than 50,000 years old o gases no longer glow and begin mixing with interstellar medium expels 5 solar masses of material into interstellar medium each year makes up 15% of mass ejected into space by stars each year means theyre going to kick off metals and some carbon and oxygen stars born after this generation will have more metallicity White Dwarf After planetary nebula you have a hot core that has held up to electron degeneracy No heating mechanism, core can only cool off at this point The exposed carbon core cools and becomes a white dwarf As the white dwarf cools it keeps its size since it is geld up to electron degeneracy Size is directly related to pressure alone Held up by electron degeneracy o Electron degeneracy not a function of temperature, is a function of pressure (Gravity) Mass-Radius Relation The more massive the white dwarf, the smaller it is Chandrasekhar limit o Upper limit to mass of white dwarf is 1.4 solar masses o Mass greater than 1.4 solar masses cannot be held up with electron degeneracy Suns Post Main Sequence Evolutionary Track Goes through AGB phase Experiences thermal pulses, thermal pulses stop when core is exposed Planetary nebula occurs and travels across the left of HR diagram, thus...
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astr3 - Stellar Corpses White Dwarfs Planetary Nebula Low...

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