User:Tohline/Apps/RotatingPolytropes

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Rotationally Flattened Polytropes

Whitworth's (1981) Isothermal Free-Energy Surface
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Earliest Efforts to Construct Equilibrium Configurations

The results of the following, chronologically listed research efforts have largely been summarized in the review by N. R. Lebovitz (1967).

  • R. Dedekind (1860), J. Reine Angew. Math., 58, 217
  • P. G. Lejeune. Dirichlet (1860), J. Reine Angel. Math., 58, 181
  • J. H. Jeans (1919) Phil. Trans. Roy. Soc., 218, 157
  • S. Chandrasekhar (1933), MNRAS, 93, 390: The equilibrium of distorted polytropes. I. The rotational problem
 

The purpose of this paper is … to extend Emden's [work] to the case of rotating gas spheres which in their non-rotating states have polytropic distributions described by the so-called Emden functions. … the gas sphere is set rotating at a constant small angular velocity <math>~\omega</math>. … we shall assume that the rotation is so slow that the configurations are only slightly oblate.

  • L. Lichtenstein (1933), Gleichgewichtsfiguren Rotierinder Flüssigkeiten (Verlag von Julius Springer, Berlin)
  • V. C. A. Ferraro (1937), MNRAS, 97, 458
  • Cowling (1941), MNRAS, 101, 367
  • P. Ledoux (1945), ApJ, 102, 143
  • Cowling & Newing (1949), ApJ, 109, 149
  • Cowling (1951), ApJ, 114, 272
  • P. Ledoux (1951), ApJ, 117, 373
  • Dive, P. (1952), Bull. Sci. Math., 76, 38
  • R. A. Lyttleton (1953), The Stability of Rotating Liquid Masses (Cambridge Univ. Press)
  • W. S. Jardetzky (1958) Theories of Figures of Celestial Bodies (Interscience, New York)
  • P. Ledoux (1958), Handbuch der Physik, 51, 605 (Flügge, S., Ed., Springer-Verlag, Berlin)
  • P. Ledoux & Th. Walraven (1958), Handbuch der Physik, 51, 353 (Flügge, S., Ed., Springer-Verlag, Berlin)
  • [ EFE Publication I ] S. Chandrasekhar (1960), J. Mathematical Analysis and Applications, 1, 240: The virial theorem in hydromagnetics
  • [ EFEPublication II ] N. R. Lebovitz (1961), ApJ, 134, 500: The virial tensor and its application to self-gravitating fluids
  • [ EFE Publication V ] S. Chandrasekhar & N. R. Lebovitz (1962a), ApJ, 135, 248: On the oscillations and the stability of rotating gaseous masses
  • [ EFE Publication X ] S. Chandrasekhar & N. R. Lebovitz (1962b), ApJ, 136, 1069: On the oscillations and the stability of rotating gaseous masses. II. The homogeneous, compressible model
  • [ EFE Publication XI ] S. Chandrasekhar & N. R. Lebovitz (1962c), ApJ, 136, 1082: On the oscillations and the stability of rotating gaseous masses. III. The distorted polytropes
 

If one assumes that the mass is distributed uniformly, the equilibrium configurations are the well-known Maclaurin spheroids. This paper will be devoted to finding the oscillation frequencies of the Maclaurin spheroids.

 

Structures have been determined for axially symmetric [uniformly] rotating gas masses, in the polytropic and white-dwarf cases … Physical parameters for the rotating configurations were obtained for values of n < 3, and for a range of white-dwarf configurations. The existence of forms of bifurcation of the axially symmetric series of equilibrium forms was also investigated. The white-dwarf series proved to lack such points of bifurcation, but they were found on the polytropic series for n < 0.808.

Example Equilibrium Configurations

Reviews

Uniform Rotation

 

Apparently, only n = 3 polytropic configurations are considered.

 

In this paper, the effects of rigid rotation on four axisymmetric modes are found for several equilibrium systems including polytopes and a 15 solar-mass stellar model. Normal modes are determined by solving directly on a two-dimensional grid the linearized dynamical equations governing adiabatic oscillations … This brute force approach has many obvious dangers, all of which are realized in practice.

  • R. Caimmi (1985), Astrophysics and Space Science, 113, 125: Emden-Chandrasekhar Axisymmetric, Rigidly Rotating Polytropes. III. Determination of Equilibrium Configurations by an Improvement of Chandrasekhar's Method

Differential Rotation

 

The oscillations of slowly rotating polytopes are treated in this paper. The initial equilibrium configurations are constructed as in Chandrasekhar (1933).

  • TORUS! J. P. Ostriker (1964), ApJ, 140, 1067: The Equilibrium of Self-Gravitating Rings
  • R. Stoeckly (1965), ApJ, 142, 208: Polytropic Models with Fast, Non-Uniform Rotation [NOTE: Article not available via SAO/NASA ADS.]
 

Models with polytropic index n = 1.5.… for the case of non-uniform rotation, no meridional currents, and axial symmetry. The angular velocity assigned … is a Gaussian function of distance from the axis. The exponential constant <math>~c</math> in this function is a parameter of non-uniformity of rotation, ranging from 0 (uniform rotation) to 1 (approximate spatial dependence of angular velocity that might arise during contraction from a uniformly rotating mass of initially homogeneous density).

For <math>~c = 0</math>, a sequence of models having increasing angular momentum is known to terminate when centrifugal force balances gravitational force at the equator; this sequence contains no bifurcation point with non-axisymmetric models as does the sequence of Maclaurin spheroids with the Jacobi ellipsoids.

For <math>~c \approx 1</math>, the distortion of interior equidensity contours of some models with fast rotation is shown to exceed that of the Maclaurin spheroids at their bifurcation point. In the absence of a rigorous stability investigation, this result suggests that a star with sufficiently non-uniform rotation reaches a point of bifurcation … Non-uniformity of rotation would then be an element bearing on star formation and could be a factor in double-star formation.

 

An explanation is given regarding the specification of various so-called <math>~n'</math> angular momentum distributions. Equilibrium models are built along the following <math>~(n, n')</math> sequences:  <math>~(0, 0)</math>, <math>~(\tfrac{3}{2}, \tfrac{3}{2})</math>, <math>~(\tfrac{3}{2}, 1)</math>, <math>~(\tfrac{3}{2}, 0)</math>, <math>~(3, 0)</math>, and <math>~(3, \tfrac{3}{2})</math>.

See Also


Whitworth's (1981) Isothermal Free-Energy Surface

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