Dynamical Models for Galactic Bars: Truncated Perfect Elliptic Disk
Abstract
de Zeeuw's perfect ellipsoid has been truncated on a surface of constant density. This truncation preserves the internal potential. A strongly triaxial case is considered, and the truncation is placed inside the bifurcation points (foci of the relevant ellipsoidal coordinates). Then the ellipsoid is projected into a two-dimensional perfect elliptic disk. The self-consistent dynamics of such disks involves only one major orbit family (box orbits) since all tube orbits reach beyond the foci, i.e., outside the truncation surface. The dynamical models for two samples of these disks have been derived numerically. The occupation frequencies are found to be positive everywhere. The dynamical solutions for these disks appear to be unique, owing to the limitation to one major orbit family. The limit of the truncated perfect elliptic disks (for the truncation approaching the center) is Freeman's disk, which itself is the projection of a uniform ellipsoid. The uniqueness of the dynamical solution for a highly triaxial truncated perfect elliptic disk suggests that the dynamics of a thin elongated nonrotating galactic bar with little density beyond the bifurcation points may be completely determined by its density figure. The same may well be true for corresponding bars with nonzero figure rotation, but this extension is outside the scope of this study.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1986
- DOI:
- 10.1086/164791
- Bibcode:
- 1986ApJ...311..511S
- Keywords:
-
- Astronomical Models;
- Barred Galaxies;
- Disk Galaxies;
- Dynamic Models;
- Elliptical Galaxies;
- Galactic Structure;
- Density Distribution;
- Galactic Rotation;
- Stellar Rotation;
- Astrophysics;
- GALAXIES: INTERNAL MOTIONS;
- GALAXIES: STRUCTURE;
- STARS: STELLAR DYNAMICS