Truncated γ-exponential models: evaporation and mass-segregation effects in the bi-component system

Abstract

ABSTRACT The γ-exponential models were previously proposed as a phenomenological attempt to characterize the properties of stellar systems with a quasi-stationary evolution under the incidence evaporation, e.g. globular clusters. They represent a parametric family of distributions that unify profiles with isothermal cores and polytropic haloes, thus providing a suitable generalization for several models available in the literature. We start our discussion revisiting some results concerning the case of single-mass systems. In particular, we emphasized that these models predict the existence of a new type of collective phenomenon: the asymptotic gravothermal collapse. This gravitational instability differs from the normal gravothermal collapse (e.g. the one associated with isothermal model) because it requires that the system releases an infinite amount of energy. Afterwards, we enter to analyse how a mass spectrum modifies the thermodynamics of these models, in particular, the associated collective phenomena. Although the theoretical description concerns to any multimass system, our computational study addresses the simplest case: the bi-component system. This analysis allows a major understanding about the thermodynamics of stellar systems under the presence of evaporation and mass segregation. For the present models, the growth of mass segregation does not affect the system evaporation disruption but favours gravothermal collapse, e.g. it tends to reduce the energy interval of stability by increasing the lower bound critical energy associated with this collective phenomenon. Extreme cases appear under certain conditions, where gravothermal collapse changes its character from asymptotic to normal.