10_-_Stellar_Structure_3

10_-_Stellar_Structure_3 - 10 Stellar Structure #3 The Plan...

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10 – Stellar Structure #3
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2 The Plan • The Lifetime of a main sequence star – Maximum age limit • Clean-up a few loose ends: – Why are MS stars stable? – High mass stars and radiation pressure – Low mass and barely alive – White Dwarfs – Brown Dwarfs
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3 Lifetime The massive stars leave the MS first and all the K & M stars ever formed are still on the MS! 3 32 The luminosity, L, of a main sequence star is: : in our approximation and if the star leaves the main sequence when a given fraction, f, of its hydrogen is gone, then : 0 LM fM f f MM τ ∝= .1 where is the main sequence lifetime.
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4 The Stability of the Sun • The mechanical time constant of the Sun is an hour or so, τ ~ 1/(G ρ ) 1/2 . The fact that no catastrophe has happened suggest (strongly) that the stability of the Sun is robust. • Our task is to understand why the Sun is so robust.
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5 First Law of Thermodynamics dQ = dU + PdV The work on the system The internal energy The heat that goes into or out of the system.
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This note was uploaded on 04/05/2009 for the course ASTRO 3332 taught by Professor Houck,j during the Spring '09 term at Cornell.

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10_-_Stellar_Structure_3 - 10 Stellar Structure #3 The Plan...

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