8 - Late Stellar Evolution and Death

8 - Late Stellar Evolution and Death - Late stellar...

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Unformatted text preview: Late stellar Evolution & Death !! Ring nebula Catseye Hubble + Chandra Cats eye nebula 3 lyr Planetary nebulae How do we get to the planetary nebulae and what happens after ?? Evolution after the main sequence : ( main sequence phase ends when H in core mostly He) 1) H burns in shell around core 3) core collapses slowly higher T 3) at 100-200 million K, 3 He C 4) red giant core He converted to C 5) outer radius increases to ~ 1 AU (100 R sun ) 7) C + He O + He Ne + He Mg + He Si synthesize heavy elements up to iron (Fe) elements Be to Fe made during these phases ! He fusion w/i core H fusion in shell surrounding core H fusion w/i core Degenerate gas (core of red giants & white dwarfs) : es (fermions) must obey Pauli exclusion no 2 es w/ same space and spin wave functions as gas compresses, es must go to higher energy states for degenerate gas, P = 1.06 x 10 13 5/3 4/3 (relativistic) [ for ideal gas, P = 8.6 x 10 14 (T / 10 7 ) ] for deg. gas , P no longer depends on T !! lose temperature regulation and stability get 10 11 L sun (absorbed in raising gas out of degeneracy) when stellar core iron (Fe), fusion can no longer generate energy to replace luminosity lost at surface star core cools collapse of star if star is massive supernova explosion binding energy (BE) of nuclei BE = m c 2 = ( m separated - m n )c 2 max. binding energy 209 Bi s-process r-process Nucelosynthesis of elements : cosmic abundances : big bang nucleosynthesis + stellar nucleosynthesis want to explain : low abundance of Li, Be, B alternating abundances (even atomic # higher) high abundance of Fe & smaller for heavier elements Mg Fe nuclear binding energy is a maximum...
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8 - Late Stellar Evolution and Death - Late stellar...

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