lec21 - Lecture 21 Energy Generation in Stars Purdue...

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Unformatted text preview: Lecture 21 Energy Generation in Stars Purdue University, Astronomy 364 1 Lecture 21 Convective Transport Lecture 21 Purdue University, Astronomy 364 2 P b b P b +dP b b +d b P P+dP +d r r+dr A blob stays in hydrostatic equilibrium with the surrounding as it rises up, P b = P , P b + dP b = P + dP Convection occurs, when b +d b < +d or d b <d , if b = The blob expands adiabatically, PV P = const Ideal Gas Lecture 21 Purdue University, Astronomy 364 3 The condition for convection requires P dP dr dr = d b d = d dr dr 1 P dP dr 1 d dr ln b = 1 ln P b + const d b b = 1 dP b P b d b = b dP b P b = dP P = P dP dr dr For ideal gas, P = m p kT dP dr = k m p dT dr + kT m p d dr = P T dT dr + P d dr Eq. of Convective Transport Lecture 21 Purdue University, Astronomy 364 4 1 d dr = 1 P dP dr 1 T dT dr 1 P dP dr 1 P dP dr 1 T dT dr dT dr 1 1 T P dP dr Convective instability: Maximum achievable temperature gradient: dT dr = 1 1 T ( r ) P ( r ) dP dr Radiative and Convective Zones Lecture 21 Purdue University, Astronomy 364 5 Equation of Energy Generation...
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lec21 - Lecture 21 Energy Generation in Stars Purdue...

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