The Steady State Wind Model for Young Stellar Clusters with an Exponential Stellar Density Distribution

TL;DR

This paper develops a hydrodynamic model for steady winds driven by young stellar clusters with exponential stellar density, highlighting the self-consistent determination of the critical transition point and effects of radiative cooling.

Contribution

It introduces a self-consistent method to locate the sonic point in stellar cluster winds with exponential density profiles, including radiative cooling effects, extending previous models.

Findings

Transition point R_sp ~ 4 R_c in negligible cooling regime

Cooling causes abrupt temperature drops and shifts the transition point inward

Model results agree with non-radiative simulations and homogeneous distributions

Abstract

A hydrodynamic model for steady state, spherically-symmetric winds driven by young stellar clusters with an exponential stellar density distribution is presented. Unlike in most previous calculations, the position of the singular point R_sp, which separates the inner subsonic zone from the outer supersonic flow, is not associated with the star cluster edge, but calculated self-consistently. When the radiative losses of energy are negligible, the transition from the subsonic to the supersonic flow occurs always at R_sp ~ 4 R_c, where R_c is the characteristic scale for the stellar density distribution, irrespective of other star cluster parameters. This is not the case in the catastrophic cooling regime, when the temperature drops abruptly at a short distance from the star cluster center and the transition from the subsonic to the supersonic regime occurs at a much smaller distance from the star cluster center. The impact from the major star cluster parameters to the wind inner structure is thoroughly discussed. Particular attention is paid to the effects which radiative cooling provides to the flow. The results of the calculations for a set of input parameters, which lead to different hydrodynamic regimes, are presented and compared to the results from non-radiative 1D numerical simulations and to those from calculations with a homogeneous stellar mass distribution.