Stellar models with isothermal cores

Abstract

This paper is devoted to the study of stellar models with isothermal cores. Two types of such configurations have been studied: (I) models with isothermal cores and polytropic envelopes (n=3) and (2) models with isothermal cores and radiative point-source envelopes with a law of opacity κ=κ_oρT^-3.5. The most important characteristic of these models is the existence of an upper limit to the fraction ν of the total mass which can be contained in the core. For models of type 2, ν_max~35%. Also it appears that, as ν increases, the radius of the star first decreases to a minimum value and then increases. Further, the luminosity of the star is found to increase by about a factor 3 from the stage when it has no isothermal core to the stage when the core contains the maximum possible mass.