The Equilibrium Series and the Secular Stability of Isothermal TwoCom ponent Star Clusters
Abstract
Secular stability of isothermal twocomponent star clusters is studied in terms of thermodynamics, by using a linearseries method. The unperturbed clusters are confined in spherical vessels. It is shown that thermodynamic treatment for the stability is possible even to selfgravitating stellar systems if the systems evolve in accordance with the FokkerPlanck equation. The applicability of the linearseries method is proved. Results of the stability analyses show that a cluster is unstable when both its selfgravitating core and the extended halo develop well. If the total mass ratio of the massive stars to the less massive ones, M2!M1, is in a certain range (the range depends on the mass ratio of the individual stars, m2!m1), the stability criteria are almost independent of the boundary conditions at the surface. This is because the less massive components behave like a heat bath to the centrally condensed selfgravitating massive components. When M2 1M1 0.25(m0/m1) , the cluster in a plastic wall with a fixed pressure has no thermodynamic equilibrium configuration bounded by its selfgravity, although it has configurations bounded by its surface pressure. This is another manifestation of Spitzer's (1969) theorem on the absence of equilibrium of isolated twocomponent clusters. Mutual relations among the secular instability, the corehalo structure, and Spitzer's (1969) theorem are discussed. Key words: Corehalo structure; Linearseries method; Secular stability; Twocomponent star clusters.
 Publication:

Publications of the Astronomical Society of Japan
 Pub Date:
 1978
 Bibcode:
 1978PASJ...30..279Y