New insight on Young Stellar Objects accretion shocks - a claim for NLTE opacities -

Description

Context. Accreted material onto CTTSs is expected to form a hot plasma structure that radiates in X-rays. Simulations of this phenomenon only partly match with observations. They all rely on the assumption that radiation and matter are decoupled, and use in addition a static model for the chromosphere.Aims. We test the validity of these two assumptions in refining the physics included in extant 1D models, and we propose guides for further improvement.Methods. We simulate accretion columns falling onto a dynamically heated stellar chromosphere using the 1D ALE code AstroLabE. This code solves the hydrodynamics equations along with the two first momenta equations for radiation transfer, with the help of a dedicated opacity table for the coupling between matter and radiation. We derive the total electron and ions densities from collisional-radiative NLTE ionization equilibrium.Results. Two main phenomena have been tested in this work. The first one is the coupling between radiation and matter and the second one is to consider a dynamical stellar atmosphere. When these phenomena are included, the net effect is a reduction of the observability of the quasi-periodic oscillations and of the total amount of X-rays received from such a structure. This last effect may be counterbalanced by a possible unburial of the whole structure.

Abstract

Submitted to A&A, revised to reflects referee's comments

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