On the orbit structure of the logarithmic potential

We investigate the dynamics in the logarithmic galactic potential with an analytical approach. The phase-space structure of the real system is approximated with resonant detuned normal forms constructed with the method based on the Lie transform, Attention is focused on the properties of the axial periodic orbits and of low-order "boxlets" that play an important role in galactic models. Using energy and ellipticity as parameters, we find analytical expressions of several useful indicators, such as stability-instability thresholds, bifurcations, and phase-space fractions of some orbit families, and compare them with numerical results available in the literature. © 2007. The American Astronomical Society. All rights reserved