Effects of Radiation in Accretion Regions of Classical T Tauri Stars: Pre-heating of accretion column in non-LTE regime

TL;DR

This study models the impact of radiation from shock-heated plasma on accretion columns in Classical T Tauri Stars, revealing that radiation absorption causes pre-shock heating and formation of a hot radiative precursor.

Contribution

It introduces a non-LTE radiation hydrodynamics model that accounts for radiation absorption and heating in accretion columns, advancing understanding of shock impact regions in young stars.

Findings

Pre-shock accreting gas heats up to 10^5 K due to radiation absorption.

A radiative precursor forms ahead of the shock with a temperature gradient.

The model shows the significance of radiation effects in accretion impact regions.

Abstract

Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns, in which optically thin and thick plasma components coexist. Thus an accurate description of these impacts requires to account for the effects of absorption and emission of radiation. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock downfalling material. We investigate if a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. We developed a radiation hydrodynamics model describing an accretion column impacting onto the surface of a Classical T Tauri Star. The model takes into account the stellar gravity, the thermal conduction, and the effects of both radiative losses and absorption of radiation by matter in the non local thermodynamic equilibrium regime. After the impact, a hot slab of post-shock plasma develops at the base of the accretion column. Part of radiation emerging from the slab is absorbed by the pre-shock accreting material. As a result, the pre-shock accretion column gradually heats up to temperatures of $10^5$ K, forming a radiative precursor of the shock. The precursor has a thermal structure with the hottest part at $T \approx 10^5$ K, with size comparable to that of the hot slab, above the post-shock region. At larger distances the temperature gradually decreases to $T \approx 10^4$ K.