Thermodynamics of the condensation of dust grains in Wolf–Rayet stellar winds

Abstract

ABSTRACT Wolf–Rayet (WR) stars are the evolutionary phases of very massive stars prior to the final supernova explosion stage. These stars lose substantial mass during the WN and WC stages. The mass losses are associated with diverse elemental and isotopic signatures that represent distinct stellar evolutionary processes. WR strong winds can host environments favourable for the condensation of dust grains with diverse compositions. The condensation of dust in the outflows of massive stars is supported by a number of observations. The present work is an attempt to develop a theoretical framework for the thermodynamics associated with the condensation of dust grains in the winds of the WN and WC phases. A novel numerical code has been developed for dust condensation. In addition to the equilibrium dust condensation calculations, we have attempted, perhaps for the first time, a set of non-equilibrium scenarios for dust condensation in various WR stages. These scenarios differ in terms of the magnitude of the non-equilibrium state, defined in terms of a simulation non-equilibrium parameter. Here, we attempt to understand the effect of the simulation non-equilibrium parameter on the condensation sequence of dust grains. In general, we found that mostly C (graphite), TiC, SiC, AlN, CaS and Fe-metal are condensed in WR winds. The extent of non-equilibrium influences the relative proportions of the earliest dust condensate compared with the condensates formed at later stages subsequent to the cooling of the gas. The results indicate that dust grains that are condensed in the WC phase may make a substantial contribution of carbon-rich dust grains to the interstellar medium.