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==Transition== In transitioning from the core to the envelope, all of the above (green) <font color="green">STEPS</font> will remain the same except for the 1<sup>st</sup> Law's treatment of the pressure. Following along the lines of our [[Appendix/Ramblings/PatrickMotl#May_5_(following_a_phone_conversation_with_Patrick)|''Ramblings'' idea exchange with Patrick Motl]], the mass-density is generically related to the pressure via the expression, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>\frac{s}{\Re/\bar{\mu}}</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \frac{1}{(\gamma_g-1)}\ln \biggl[ \frac{P}{(\gamma_g-1)\rho^{\gamma_g}} \biggr] </math> </td> </tr> <tr> <td align="right"> <math>\Rightarrow ~~~ \frac{s \bar\mu (\gamma_g-1)}{\Re}</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \ln \biggl[ \frac{P}{(\gamma_g-1)\rho^{\gamma_g}} \biggr] </math> </td> </tr> <tr> <td align="right"> <math> \Rightarrow ~~~P </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>(\gamma_g - 1) \rho^{\gamma_g}\exp \biggl[\frac{s \bar\mu (\gamma_g-1)}{\Re}\biggr]\, .</math> </td> </tr> </table> Given that, in polytropic configurations for which we make the association, <math>\gamma_g = (n+1)/n</math>, the pressure is related to the density via the expression, <math>P = K\rho^{\gamma_g}</math>, we appreciate that, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>K</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> (\gamma_g - 1) \exp \biggl[\frac{s \bar\mu (\gamma_g-1)}{\Re}\biggr] \, . </math> </td> </tr> </table> ===Core=== For the core, we set <math>\gamma_g = 6/5</math>. Hence, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> P </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>K_c \rho^{6/5} \, .</math> </td> </tr> </table> Normalizing the pressure and the density as we have in [[SSC/Structure/BiPolytropes/Analytic51#Normalization|a closely related discussion of the structure of bipolytropes]], we have throughout the core, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> P^* = \frac{P}{K_c\rho_0^{6/5}} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>(\rho^*)^{6/5} \, .</math> </td> </tr> </table> Now, in this normalized expression we see that the polytropic constant for the core is, <math>K^*_c = 1</math>. This means that the specific entropy of all the fluid in the core is given by the expression, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>1</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \frac{1}{5} \exp \biggl[\frac{s^*_c {\bar\mu}_c }{5\Re}\biggr] </math> </td> </tr> <tr> <td align="right"> <math>\Rightarrow ~~~ \frac{s^*_c {\bar\mu}_c }{\Re}</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> 5\ln(5 ) \, . </math> </td> </tr> </table> ===Envelope=== For the envelope, we set <math>\gamma_g = 2</math>. Hence, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> P </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>K_e \rho^{2} \, .</math> </td> </tr> </table> Adopting the same pressure and density normalizations as used in the core, we have throughout the envelope, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> P^* = \frac{P}{K_c\rho_0^{6/5}} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\biggl(\frac{K_e}{K_c} \biggr) \rho_0^{4/5} (\rho^*)^2 \, .</math> </td> </tr> </table> Now, at the [[SSC/Structure/BiPolytropes/Analytic51#Step_5:_Interface_Conditions|interface of the equilibrium model]], we know that, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \frac{K_e}{K_c} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \rho_0^{-4/5}\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \theta^{-4}_i = \rho_0^{-4/5}\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \biggl[1 + \frac{\xi_i^2}{3}\biggr]^2 \, . </math> </td> </tr> </table> Hence, throughout the envelope, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> P^* </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \biggl[1 + \frac{\xi_i^2}{3}\biggr]^2 (\rho^*)^2 \, , </math> </td> </tr> </table> in which case we find, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>K^*_e</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \biggl[1 + \frac{\xi_i^2}{3}\biggr]^2 </math> </td> </tr> <tr> <td align="right"> <math> \Rightarrow ~~~ \frac{s^*_e \bar\mu_e}{\Re} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \ln\biggl\{ \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \biggl[1 + \frac{\xi_i^2}{3}\biggr]^2 \biggr\} \, . </math> </td> </tr> </table> ===<font color="green">STEP 3</font> Clarification=== It is critically important to appreciate that the manner in which the pressure is determined at discrete locations in our finite-difference model must be different in the envelope and the core. Keeping in mind that, in general, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> P </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>(\gamma_g - 1) \rho^{\gamma_g}\exp \biggl[\frac{s \bar\mu (\gamma_g-1)}{\Re}\biggr]\, ,</math> </td> </tr> </table> for <math>(n_c, n_e) = (5, 1)</math> bipolytropes, we have … <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> Core <math>(\gamma_g=6/5)</math>: <math>P_{j-1/2}</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \frac{1}{5}\biggl[ {\bar\rho}_{j-1/2}\biggr]^{6/5} \cdot \exp\biggl[ \frac{\mu_c s^*_c}{5\mathfrak{R}} \biggr] = \biggl[ {\bar\rho}_{j-1/2}\biggr]^{6/5} \, . </math> </td> </tr> <tr> <td align="right"> Envelope <math>(\gamma_g=2)</math>: <math>P_{j-1/2}</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl[ {\bar\rho}_{j-1/2}\biggr]^{2} \cdot \exp\biggl[ \frac{\mu_e s^*_e}{\mathfrak{R}} \biggr] = \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \biggl[1 + \frac{\xi_i^2}{3}\biggr]^2 \biggl[ {\bar\rho}_{j-1/2}\biggr]^{2} \, . </math> </td> </tr> </table> ===Interface=== Drawing from our [[SSC/Structure/BiPolytropes/Analytic51|chapter in which the bipolytrope is constructed]], we note the following determination of the density and pressure at the interface, as viewed from the perspective of the core and, separately, from the perspective of the envelope. <table border="1" align="center"> <tr> <td align="center" colspan="2"> Properties at the (Unperturbed) Interface </td> </tr> <tr> <td align="center" width="50%"> <b>Core</b><br /> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \frac{s^*_c \bar\mu_c}{\Re} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> 5\ln(5) </math> </td> </tr> </table> </td> <td align="center"> <b>Envelope</b><br /> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \frac{s^*_e \bar\mu_e}{\Re} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \ln\biggl\{ \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \theta_i^{-4} \biggr\} </math> </td> </tr> </table> </td> </tr> <tr> <td align="left"> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>(\rho^*)_i </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\theta_i^5</math> </td> </tr> <tr> <td align="right"> <math> (P^*)_i </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\frac{1}{5} (\rho^*)_i^{6/5}\exp \biggl[\frac{s_c \bar\mu_c }{5\Re}\biggr]</math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>(\rho^*)_i^{6/5}</math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\theta_i^{6}</math> </td> </tr> </table> </td> <td align="left"> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>(\rho^*)_i </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\biggl( \frac{\mu_e}{\mu_c} \biggr) \theta_i^5</math> </td> </tr> <tr> <td align="right"> <math> (P^*)_i </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>(\rho^*)_i^{2}\exp \biggl[\frac{s_e \bar\mu_e }{\Re}\biggr]</math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>(\rho^*)_i^{2}\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \theta_i^{-4} </math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\theta_i^6</math> </td> </tr> </table> </td> </tr> </table> ---- In what follows, we will continue to focus on the interface but, for simplicity, will drop the "i" subscript; instead, we will use a "0" subscript to indicate a property at the ''unperturbed'' interface. <table border="1" align="center"> <tr> <td align="center" colspan="2"> Properties at the ''Perturbed Interface </td> </tr> <tr> <td align="center" width="50%"> <b>Core</b><br /> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \frac{s^*_c \bar\mu_c}{\Re} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> 5\ln(5) </math> </td> </tr> </table> </td> <td align="center"> <b>Envelope</b><br /> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \frac{s^*_e \bar\mu_e}{\Re} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \ln\biggl\{ \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \theta_i^{-4} \biggr\} </math> </td> </tr> </table> </td> </tr> <tr> <td align="left"> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>\rho^*_c = (\rho^*_c)_0 + (\delta \rho)_c </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\theta_i^5 + (\delta \rho)_c</math> </td> </tr> <tr> <td align="right"> <math> P^*_c = (P^*_c)_0 + (\delta P)_c </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\biggl[ \rho^*_c \biggr]^{6/5}</math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\biggl[\theta_i^5 + (\delta \rho)_c\biggr]^{6/5}</math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>\approx</math> </td> <td align="left"> <math>\theta_i^6\biggl[1 + \frac{6(\delta \rho)_c}{5\theta_i^5}\biggr]</math> </td> </tr> <tr> <td align="right"> <math>\Rightarrow ~~~ (\delta P)_c</math> </td> <td align="center"> <math>\approx</math> </td> <td align="left"> <math>\frac{6\theta_i(\delta \rho)_c}{5}</math> </td> </tr> <tr> <td align="right"> <math>\Rightarrow ~~~ p_c \equiv \frac{(\delta P)_c}{(P^*_c)_0}</math> </td> <td align="center"> <math>\approx</math> </td> <td align="left"> <math>\frac{6(\delta \rho)_c}{5\theta_i^5}</math> </td> </tr> </table> </td> <td align="left"> <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>\rho^*_e = (\rho^*_e)_0 + (\delta\rho)_e</math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\biggl( \frac{\mu_e}{\mu_c} \biggr) \theta_i^5+ (\delta\rho)_e</math> </td> </tr> <tr> <td align="right"> <math> P^*_e = (P^*_e)_0 + (\delta P)_e </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math>\biggl[ \rho^*_e \biggr]^{2}\exp \biggl[\frac{s_e \bar\mu_e }{\Re}\biggr]</math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl[ \biggl( \frac{\mu_e}{\mu_c} \biggr) \theta_i^5+ (\delta\rho)_e\biggr]^{2} \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-2} \theta_i^{-4} </math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>\approx</math> </td> <td align="left"> <math>\theta_i^6\biggl[ 1 + 2(\delta\rho)_e \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-1} \theta_i^{-5}\biggr]</math> </td> </tr> <tr> <td align="right"> <math>\Rightarrow ~~~ (\delta P)_e</math> </td> <td align="center"> <math>\approx</math> </td> <td align="left"> <math>2(\delta\rho)_e \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-1} \theta_i</math> </td> </tr> <tr> <td align="right"> <math>\Rightarrow ~~~ p_e \equiv \frac{(\delta P)_e}{(P^*_e)_0}</math> </td> <td align="center"> <math>\approx</math> </td> <td align="left"> <math>\frac{2(\delta\rho)_e}{\theta_i^5} \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-1} </math> </td> </tr> </table> </td> </tr> </table> Now, in order for <math>(\delta P)_c = (\delta P)_e</math> at the interface, we must have, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> 2(\delta\rho)_e \biggl( \frac{\mu_e}{\mu_c} \biggr)^{-1} \theta_i </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \frac{6\theta_i(\delta \rho)_c}{5} </math> </td> </tr> <tr> <td align="right"> <math> \Rightarrow ~~~(\delta\rho)_e </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \frac{3}{5}\biggl( \frac{\mu_e}{\mu_c} \biggr) (\delta \rho)_c </math> </td> </tr> <tr> <td align="right"> <math> \Rightarrow ~~~\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-1} \frac{(\delta\rho)_e }{\theta_i^5} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl(\frac{3}{5}\biggr) \frac{(\delta \rho)_c}{\theta_i^5} </math> </td> </tr> <tr> <td align="right"> <math> \Rightarrow ~~~\biggl[ \frac{(\delta\rho)}{\rho^*_0} \biggr]_e </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl(\frac{3}{5}\biggr) \biggl[ \frac{(\delta\rho)}{\rho^*_0} \biggr]_c </math> </td> </tr> <tr> <td align="right"> <math> \Rightarrow ~~~d_e </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl(\frac{\gamma_c}{\gamma_e}\biggr) d_c \, . </math> </td> </tr> </table> We also know that, according to the linearized equation of continuity, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \biggl[r_0 \frac{dx}{dr_0} + 3x + d \biggr]_e </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl[r_0 \frac{dx}{dr_0} + 3x + d \biggr]_c \, . </math> </td> </tr> </table> Given that, at the interface, <math>x_e = x_c</math>, this means that, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \biggl[r_0 \frac{dx}{dr_0}\biggr]_e </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl[r_0 \frac{dx}{dr_0}\biggr]_c - \biggl[\biggl(\frac{\gamma_c}{\gamma_e}\biggr)- 1\biggr] d_c </math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \biggl[r_0 \frac{dx}{dr_0}\biggr]_c + \biggl[\biggl(\frac{\gamma_c}{\gamma_e}\biggr)- 1\biggr] \biggl\{ \biggl[r_0 \frac{dx}{dr_0}\biggr]_c + 3x \biggr\} </math> </td> </tr> <tr> <td align="right"> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> 3x\biggl[\biggl(\frac{\gamma_c}{\gamma_e}\biggr)- 1\biggr] + \biggl(\frac{\gamma_c}{\gamma_e}\biggr) \biggl[r_0 \frac{dx}{dr_0}\biggr]_c \, ; </math> </td> </tr> </table> or, dividing through by <math>x</math>, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \biggl[\frac{d\ln x}{d\ln r_0}\biggr]_e </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> 3\biggl[\biggl(\frac{\gamma_c}{\gamma_e}\biggr)- 1\biggr] + \biggl(\frac{\gamma_c}{\gamma_e}\biggr) \biggl[\frac{d\ln x}{d\ln r_0}\biggr]_c \, . </math> </td> </tr> </table> This exactly matches the interface constraint presented in [[SSC/Stability/BiPolytropes#Interface_Conditions|a related discussion in a separate chapter]]. Now, as has already been stated in [[#Step_5|Step 5, above]], for our analytic guess for the core's displacement function, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>\biggl[\frac{d\ln x}{d\ln r_0}\biggr]_c</math> </td> <td align="center"> <math>=</math> <td align="left"> <math> \biggl(\frac{2}{15}\biggr) \xi^2 \biggl[\frac{\xi^2}{15}-1\biggr]^{-1} = 2.4526969 \, ; </math> </td> </tr> <tr> <td align="right"> <math>\Rightarrow ~~~ \biggl[\frac{d\ln x}{d\ln r_0}\biggr]_e</math> </td> <td align="center"> <math>=</math> <td align="left"> <math> 0.2716182 \, . </math> </td> </tr> </table> where the numerical evaluation has been presented specifically for the core/envelope interface of the critical "Model A" configuration in which, <math>\xi_i = 9.0149598</math>. Also, given that, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math> \frac{x}{r_0} </math> </td> <td align="center"> <math>=</math> </td> <td align="left"> <math> \frac{\alpha_\mathrm{scale}}{\xi} \biggl(\frac{2\pi}{3}\biggr)^{1 / 2} \biggl[1 - \frac{\xi^2}{15}\biggr] = (-\alpha_\mathrm{scale}) \cdot 0.7092314 \, , </math> </td> </tr> </table> we find that, <table border="0" cellpadding="5" align="center"> <tr> <td align="right"> <math>\biggl[\frac{dx}{dr_0}\biggr]_c</math> </td> <td align="center"> <math>=</math> <td align="left"> <math> (-\alpha_\mathrm{scale}) \cdot 1.7395297 \, ; </math> </td> </tr> <tr> <td align="right"> <math>\biggl[\frac{d x}{d r_0}\biggr]_e</math> </td> <td align="center"> <math>=</math> <td align="left"> <math> (-\alpha_\mathrm{scale}) \cdot 0.1926402 \, . </math> </td> </tr> </table>
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