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Title:
Thermodynamic Description of a Family of Partially Relaxed Stellar Systems
Authors:
Bertin, G.; Trenti, M.
Affiliation:
AA(Dipartimento di Fisica, Università di Milano, Via Celoria 16, I-20133 Milan, Italy; ), AB(Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy; )
Publication:
The Astrophysical Journal, Volume 584, Issue 2, pp. 729-734. (ApJ Homepage)
Publication Date:
02/2003
Origin:
UCP
ApJ Keywords:
Galaxies: Evolution, Galaxies: Formation, Galaxies: Kinematics and Dynamics, Galaxies: Structure, Stellar Dynamics
DOI:
10.1086/345889
Bibliographic Code:
2003ApJ...584..729B

Abstract

We examine the thermodynamic properties of a family of partially relaxed, anisotropic stellar systems, derived earlier from the Boltzmann entropy under the assumption that a third quantity Q is conserved in addition to the total energy and the total number of stars. We now show that the family of models conforms to the paradigm of the gravothermal catastrophe, which is expected to occur (in the presence of adequate energy transport mechanisms) when the one-parameter equilibrium sequence attains sufficiently high values of the concentration parameter; these are the values for which the models are well fitted by the R1/4 law. In the intermediate concentration regime the models belonging to the sequence exhibit significant deviations from the R1/4 law. Curiously, in the low-concentration regime, the global thermodynamic temperature associated with the models becomes negative when the models become too anisotropic so that they are unstable against the radial orbit instability; this latter behavior, while offering a new clue to the physical interpretation of the radial orbit instability, is at variance with respect to the low-concentration limit of the classical case of the isotropic, isothermal sphere investigated by Bonnor and Lynden-Bell & Wood.
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