Physical and radiative properties of the first-core accretion shock

Abstract

Radiative shocks play a dominant role in star formation. The accretion shocks on the first and second Larson's cores involve radiative processes and are thus characteristic of radiative shocks. In this study, we explore the formation of the first Larson's core and characterize the radiative and dynamical properties of the accretion shock, using both analytical and numerical approaches. We develop both numerical RHD calculations and a semi-analytical model that characterize radiative shocks in various physical conditions, for radiating or barotropic fluids. Then, we perform 1D spherical collapse calculations of the first Larson's core, using a grey approximation for the opacity of the material. We consider three different models for radiative transfer, namely: the barotropic approximation, the FLD approximation and the more complete M1 model. We investigate the characteristic properties of the collapse and of the first core formation. Comparison between the numerical results and our semi-analytical model shows that this latter reproduces quite well the core properties obtained with the numerical calculations. The accretion shock on the first Larson core is found to be supercritical, implying that all the accretion shock energy on the core is radiated away. The FLD approximation is found to agree quite well with the results based on the M1 model, and is thus appropriate to study the star formation process. In contrast, the barotropic approximation does not correctly describe the thermal properties of the gas during the collapse. We show that a consistent treatment of radiation and hydrodynamics is mandatory to correctly handle the cooling of the gas during the core formation and thus to obtain the correct mechanical and thermal properties for this latter.