Oscillations of MHD shock waves on the surfaces of T Tauri stars

TL;DR

This paper investigates the stability and oscillations of magnetohydrodynamic shock waves on T Tauri star surfaces, considering arbitrary magnetic field angles and radiative losses, revealing conditions for shock stability and oscillation periods.

Contribution

It introduces a model for MHD shock waves with arbitrary magnetic field inclination and analyzes their stability and oscillation behavior in the context of T Tauri stars.

Findings

Shock wave oscillation periods are 0.02-0.2 seconds.

A stability criterion for radiative shock waves is established.

Magnetic field inclination affects shock stability.

Abstract

This work treats the matter deceleration in a magnetohydrodynamics radiative shock wave at the surface of a star. The problem is relevant to classical T Tauri stars where infalling matter is channeled along the star's magnetic field and stopped in the dense layers of photosphere. A significant new aspect of the present work is that the magnetic field has an arbitrary angle with respect to the normal to the star's surface. We consider the limit where the magnetic field at the surface of the star is not very strong in the sense that the inflow is super Alfv\'enic. In this limit the initial deceleration and heating of plasma (at the entrance to the cooling zone) occurs in a fast magnetohydrodynamic shock wave. To calculate the intensity of radiative losses we use "real" and "power-law" radiative functions. We determine the stability/instability of the radiative shock wave as a function of parameters of the incoming flow: velocity, strength of the magnetic field, and its inclination to the surface of the star. In a number of simulation runs with the "real" radiative function, we find a simple criterion for stability of the radiative shock wave. For a wide range of parameters, the periods of oscillation of the shock wave are of the order 0.02-0.2 sec.