Editing SSC/Structure/BiPolytropes/FreeEnergy51 (section)

===The Envelope===

Similarly, the energy contained in the envelope's thermodynamic reservoir may be written as,
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<math>~\biggl( \frac{\mathfrak{S}_A}{E_\mathrm{norm}} \biggr)_\mathrm{env}</math>
  </td>
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<math>~=</math>
  </td>
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<math>
\frac{2}{3({\gamma_e}-1)} \biggl( \frac{\chi}{\chi_\mathrm{eq}} \biggr)^{3-3\gamma_e} \biggl( \frac{P_{ie}}{P_{ic}} \biggr)
\biggl[ \frac{2\pi P_{ic} \chi^3}{P_\mathrm{norm}} \biggr]_\mathrm{eq}  
\biggl[ (1-q^3) s_\mathrm{env} \biggr] \, ,
</math>
  </td>
</tr>
</table>
</div>
where,
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<math>~(1-q^3) s_\mathrm{env} </math>
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<math>~\equiv</math>
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<math>~ 
\int_q^1  3\biggl[ 1 - p_e(x) \biggr]  x^2 dx \, ,
</math>
  </td>
</tr>
</table>
</div>
defines the relevant integral over the envelope's pressure distribution.  According to our [[SSC/Structure/BiPolytropes/Analytic51#Profile|derivation of the properties of detailed force-balance <math>~(n_c, n_e) = (5, 1)</math> bipolytropes]] &#8212; see also the relevant derivations [[SSC/BipolytropeGeneralizationVersion2#Bipolytrope_Generalization|in our accompanying overview]] &#8212;  the pressure throughout the envelope is defined by the dimensionless function,
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<math>~P^* \equiv \frac{P_\mathrm{env}(\eta)}{P_0} </math>
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<math>~=</math>
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<math>~\theta_i^6 \phi^2(\eta) = \theta_i^6 \biggl( \frac{A}{\eta} \biggr)^2 \sin^2(\eta-B) \, ,</math>
  </td>
</tr>

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<math>\Rightarrow ~~~~ 1-p_e(x) \equiv \frac{P_\mathrm{env}(x)}{P_{ie}} 
</math>
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<math>~=</math>
  </td>
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<math>~
\biggl( \frac{P_{ic}}{P_{ie}}  \biggr) \biggl( \frac{P_0}{P_{ic}}  \biggr) \frac{P_\mathrm{env}(x)}{P_0} 
</math>
  </td>
</tr>

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&nbsp;
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<math>~=</math>
  </td>
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<math>~
\biggl( \frac{P_{ic}}{P_{ie}}  \biggr) \biggl( \theta_i^{-6} \biggr) \theta_i^6 \biggl( \frac{A}{b_\eta x} \biggr)^2 \sin^2(b_\eta x-B) \, ,
</math>
  </td>
</tr>

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&nbsp;
  </td>
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<math>~=</math>
  </td>
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<math>~
\biggl( \frac{P_{ic}}{P_{ie}}  \biggr) \biggl( \frac{A}{b_\eta} \biggr)^2 \frac{\sin^2(b_\eta x-B)}{x^2} \, ,
</math>
  </td>
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</div>
where, <math>~b_\eta</math> has been defined above in connection with our [[SSC/Structure/BiPolytropes/FreeEnergy51#The_Envelope|derivation of the envelope's mass profile]].  The desired integral over this pressure distribution therefore gives,
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<math>~(1-q^3)s_\mathrm{env}</math>
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<math>~=</math>
  </td>
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<math>~
3 \biggl( \frac{P_{ic}}{P_{ie}}  \biggr) \biggl( \frac{A}{b_\eta} \biggr)^2 \int_q^1 \sin^2(b_\eta x-B) dx
</math>
  </td>
</tr>

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&nbsp;
  </td>
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<math>~=</math>
  </td>
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<math>~
\frac{3}{4} \biggl( \frac{P_{ic}}{P_{ie}}  \biggr) \biggl( \frac{A^2}{b_\eta^3} \biggr) \biggl[ 2b_\eta x -\sin[2(b_\eta x - B)] \biggr]_q^1 \, ,
</math>
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</tr>
</table>
</div>
where, as before, we have dropped the integration constant because it cancels upon insertion of the specified integration limits.  Therefore, we have,
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  <td align="right">
<math>~\biggl( \frac{\mathfrak{S}_A}{E_\mathrm{norm}} \biggr)_\mathrm{env}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\frac{2}{3({\gamma_e}-1)} \biggl( \frac{\chi}{\chi_\mathrm{eq}} \biggr)^{3-3\gamma_e} 
\biggl[ \frac{2\pi P_{ic} \chi^3}{P_\mathrm{norm}} \biggr]_\mathrm{eq}  
\frac{3}{4} \biggl( \frac{A^2}{b_\eta^3} \biggr) \biggl[ 2b_\eta x -\sin[2(b_\eta x - B)] \biggr]_q^1  \, .
</math>
  </td>
</tr>
</table>
</div>
Now, drawing from our above derivation steps and discussion, we know that,
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<math>~b_\eta</math>
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<math>~=</math>
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<math>~3^{1/2} \biggl( \frac{\mu_e}{\mu_c} \biggr) \frac{\theta_i^2 \xi_i}{q} \, ,</math>
  </td>
</tr>
</table>
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and
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<math>\frac{2\pi P_{ic} \chi_\mathrm{eq}^3}{P_\mathrm{norm}} </math>
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<math>~=</math>
  </td>
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<math>
\biggl( \frac{3^6}{2\pi} \biggr)^{1/2} \biggl(1 + a_\xi q^2 \biggr)^{-3} a_\xi^{3/2} = \biggl( \frac{3^3}{2\pi} \biggr)^{1/2} \biggl( \frac{\theta_i^2\xi_i }{q}\biggr)^3 \, .
</math>
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</tr>
</table>
</div>

Finally, then, we can write,

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  <td align="right">
<math>~\biggl( \frac{\mathfrak{S}_A}{E_\mathrm{norm}} \biggr)_\mathrm{env}</math>
  </td>
  <td align="center">
<math>~=</math>
  </td>
  <td align="left">
<math>
\frac{2}{3({\gamma_e}-1)} \biggl( \frac{\chi}{\chi_\mathrm{eq}} \biggr)^{3-3\gamma_e} \biggl\{
\frac{3}{4} A^2\biggl[ \biggl( \frac{3^3}{2\pi} \biggr)^{1/2} \biggl( \frac{\theta_i^2\xi_i }{q}\biggr)^3 \biggr] 
\biggl[ 3^{1/2} \biggl( \frac{\mu_e}{\mu_c} \biggr) \frac{\theta_i^2 \xi_i}{q} \biggr]^{-3} \biggl[ 2b_\eta x -\sin[2(b_\eta x - B)] \biggr]_q^1  \biggr\}
</math>
  </td>
</tr>

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&nbsp;
  </td>
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<math>~=</math>
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<math>
\frac{2}{3({\gamma_e}-1)} \biggl( \frac{\chi}{\chi_\mathrm{eq}} \biggr)^{3-3\gamma_e} \biggl\{
\biggl( \frac{\mu_e}{\mu_c} \biggr)^{-3} A^2  \biggl( \frac{3^2}{2^5\pi} \biggr)^{1/2}  \biggl[ 2b_\eta x -\sin[2(b_\eta x - B)] \biggr]_q^1  \biggr\} \ .
</math>
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</table>
</div>
The term inside the curly brackets precisely matches the analytic expression for the dimensionless thermal energy of the envelope, <math>~S^*_\mathrm{env}</math>, that has been derived elsewhere in conjunction with our [[SSC/Structure/BiPolytropes/Analytic51#Expression_for_Free_Energy|discussion of the detailed force-balanced structure of this bipolytrope]].