Difference between revisions of "User:Tohline/SSC/Structure/Other Analytic Models"
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==Linear Density Distribution== | ==Linear Density Distribution== | ||
In an article titled, "Stellar Evolution: A Survey with Analytic Models," [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660024135.pdf R. F. Stein] (1966, in ''Stellar Evolution, Proceedings of an International Conference held at the Goddard Space Flight Center, Greenbelt, MD, U.S.A., edited by R. F. Stein & A. G. W. Cameron, pp. 1-105) defines the "Linear Stellar Model" as a star whose density "varies linearly from the center to the surface," that is, | In an article titled, "Stellar Evolution: A Survey with Analytic Models," [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660024135.pdf R. F. Stein] (1966, in ''Stellar Evolution, Proceedings of an International Conference held at the Goddard Space Flight Center, Greenbelt'', MD, U.S.A., edited by R. F. Stein & A. G. W. Cameron, pp. 1-105) defines the "Linear Stellar Model" as a star whose density "varies linearly from the center to the surface," that is, | ||
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<math>\rho(r) = \rho_c\biggl( 1 - \frac{r}{R} \biggr) \, ,</math> | <math>\rho(r) = \rho_c\biggl( 1 - \frac{r}{R} \biggr) \, ,</math> | ||
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<math>~\frac{4\pi\rho_c^2 r}{3} \biggl( 1 - \frac{r}{R} \biggr) \biggl[1 - \frac{3}{4} \biggl( \frac{r}{R} \biggr)\biggr] \, .</math> | <math>~\frac{4\pi G \rho_c^2 r}{3} \biggl( 1 - \frac{r}{R} \biggr) \biggl[1 - \frac{3}{4} \biggl( \frac{r}{R} \biggr)\biggr] \, .</math> | ||
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Revision as of 23:42, 19 June 2015
Other Analytically Definable, Spherical Equilibrium Models
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Linear Density Distribution
In an article titled, "Stellar Evolution: A Survey with Analytic Models," R. F. Stein (1966, in Stellar Evolution, Proceedings of an International Conference held at the Goddard Space Flight Center, Greenbelt, MD, U.S.A., edited by R. F. Stein & A. G. W. Cameron, pp. 1-105) defines the "Linear Stellar Model" as a star whose density "varies linearly from the center to the surface," that is,
<math>\rho(r) = \rho_c\biggl( 1 - \frac{r}{R} \biggr) \, ,</math>
where, <math>~\rho_c</math> is the central density and, <math>~R</math> is the radius of the star. Both the mass distribution and the pressure distribution can be obtained analytically from this specified density distribution. Specifically, following our general solution strategy for determining the equilibrium structure of spherically symmetric, self-gravitating configurations,
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<math>~M_r(r)</math> |
<math>~=</math> |
<math>~\int_0^r 4\pi r^2 \rho(r) dr</math> |
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<math>~=</math> |
<math>~\frac{4\pi\rho_c r^3}{3} \biggl[1 - \frac{3}{4} \biggl( \frac{r}{R} \biggr)\biggr] \, ,</math> |
in which case we can write,
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<math>~g_0(r) \equiv \frac{G M_r(r) \rho(r)}{r^2} </math> |
<math>~=</math> |
<math>~\frac{4\pi G \rho_c^2 r}{3} \biggl( 1 - \frac{r}{R} \biggr) \biggl[1 - \frac{3}{4} \biggl( \frac{r}{R} \biggr)\biggr] \, .</math> |
Hence, proceeding via what we have labeled as "Technique 1", and enforcing the surface boundary condition, <math>~P(R) = 0</math>, Stein (1966) determines that,
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<math>~P(r)</math> |
<math>~=</math> |
<math>~- \int_0^r g_0(r) dr</math> |
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<math>~=</math> |
<math>~\frac{\pi G\rho_c^2 R^2}{36} \biggl[5 - 24 \biggl( \frac{r}{R} \biggr)^2 + 28 \biggl( \frac{r}{R} \biggr)^3 - 9 \biggl( \frac{r}{R} \biggr)^4 \biggr] \, ,</math> |
where, it can readily be deduced, as well, that the central pressure is,
<math>~P_c = \frac{5\pi}{36} G\rho_c^2 R^2 \, .</math>
Parabolic Density Distribution
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