title: Caloric curve of star clusters.
abstract: Self-gravitating systems, such as globular clusters or elliptical galaxies, are the prototypes of many-body systems with long-range interactions, and should be the natural arena in which to test theoretical predictions on the statistical behavior of long-range-interacting systems. Systems of classical self-gravitating particles can be studied with the standard tools of equilibrium statistical mechanics, provided the potential is regularized at small length scales and the system is confined in a box. The confinement condition looks rather unphysical in general, so that it is natural to ask whether what we learn with these studies is relevant to real self-gravitating systems. In order to provide an answer to this question, we consider a basic, simple, yet effective model of globular clusters: the King model. This model describes a self-consistently confined system, without the need of any external box, but the stationary state is a nonthermal one. In particular, we consider the King model with a short-distance cutoff on the interactions, and we discuss how such a cutoff affects the caloric curve, i.e., the relation between temperature and energy. We find that the cutoff stabilizes a low-energy phase, which is absent in the King model without cutoff; the caloric curve of the model with cutoff turns out to be very similar to that of previously studied confined and regularized models, but for the absence of a high-energy gaslike phase. We briefly discuss the possible phenomenological as well as theoretical implications of these results.
authors.affiliation: Dipartimento di Fisica e Astronomia and Centro per lo Studio delle Dinamiche Complesse (CSDC), Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (FI), Italy. lapo.casetti@unifi.it
authors.forename: Lapo
authors.initials: L
authors.lastname: Casetti
authors.forename: Cesare
authors.initials: C
authors.lastname: Nardini
mesh_terms: D002151:Calorimetry; D003198:Computer Simulation; D004735:Energy Transfer; D008956:Models, Chemical; D055609:Stars, Celestial / Q000737:chemistry*; D013816:Thermodynamics