Fokker-Planck Models for Rotating Stellar Systems

Abstract

Observations of Globular Cluster ellipticity distributions related to some fundamental parameters give strong evidence for a decay of rotational energy in these systems with time. In order to study the effectiveness of angular momentum transport (or loss, resp.) a code has been written which solves the Fokker-Planck equation in (E, Jz)-space and follows the evolution from some initial conditions through core collapse (and possibly gravothermal oscillations) up to the post-collapse phase. For the purpose of comparability with N-body simulations rotating initial model configurations according to the prescriptions of Lupton & Gunn (1987) have been constructed. These models are intended to continue previous work by Goodman (1983, Fokker-Planck) and Akiyama & Sugimoto (1989, N-Body). In this contribution the derivation of the flux coefficients is given.

Astrophysical N-Body Simulations: Algorithms and Challenges

“…Recent models of that type include the effects of anisotropy (differences between radial and tangential velocity dispersion, which can be present even in spherical systems, Takahashi 1996Takahashi , 1997. Another improvement includes for the first time the effect of rotation for those of the globular clusters which are slightly flattened (Einsel & Spurzem 1997). Also anisotropic gaseous models based on a moment evaluation of the Fokker-Planck equation were successfully used (Louis & Spurzem 1991, Spurzem 1994).…”

Applications of a Parallel Hybrid N–body SCF Code

“…There is an N -body approach by Arabadjis & Richstone (1998ab) using a TREE-code. We have undertaken an effort to use a simplified (2 integrals of motion, equal masses) 2D-Fokker-Planck model to follow the evolution of self-gravitating, rotating star clusters into core collapse without central mass (Einsel & Spurzem 1998). The gravo-gyro catastrophe, earlier postulated by Hachisu (1979) by using a linear stability analysis, has been rediscovered, followed by a self-similar contraction phase.…”

Stellar Evolution and Dynamics in Star Clusters

“…Some models already include mutual interaction between stellar evolution and star cluster dynamics (see Chernoff & Weinberg 1990;Fukushige & Heggie 1995;de la Fuente Marcos 1996;Spurzem & Aarseth 1996;Einsel & Spurzem 1997;Portegies Zwart et al 1997;Tout et al 1997, and the reviews Hut et al 1992 andHeggie 1997). Here we study the arguments for combining stellar evolution and stellar dynamics in hybrid models, the advantages and disadvantages of performing such model computations and outline the future of dynamical models of star clusters.…”