Thermodynamics of the Condensation of Dust Grains in Wolf-Rayet Stellar Winds

TL;DR

This paper develops a thermodynamic and numerical framework to study dust grain condensation in Wolf-Rayet star winds, including non-equilibrium scenarios, revealing the potential contribution of these stars to interstellar dust.

Contribution

It introduces a novel numerical code for dust condensation, including the first exploration of non-equilibrium effects in WR star wind environments.

Findings

Carbon-rich dust grains are likely condensed in WR winds.

Non-equilibrium conditions affect the timing and composition of dust formation.

Dust from WC phases may significantly enrich the interstellar medium.

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 WN and WC stages. The mass losses are associated with diverse elemental and isotopic signatures that represent distinct stellar evolutionary processes. The WR strong winds can host environments for condensation of dust grains with diverse compositions. The condensation of dust in the outflows of the massive stars is supported by several observations. The present work is an attempt to develop a theoretical framework of thermodynamics associated with the condensation of dust grains in the winds of WN and WC phases. A novel numerical code has been developed for dust condensation. Apart from 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 sensitivity 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 earliest dust condensate compared to the condensates formed at later stages subsequent to the cooling of the gas. The results indicate that dust grains condensed in the WC phase may substantially contribute carbon-rich dust grains to the interstellar medium.