Line formation in the inner winds of classical T Tauri stars: testing the conical-shell wind solution

TL;DR

This study models the emission line profiles of hydrogen and helium in classical T Tauri stars using axisymmetric MHD simulations, showing the conical-shell wind's role in observed spectral features and testing the model's consistency with observations.

Contribution

It extends previous conical-shell wind models by including a magnetospheric accretion funnel and predicts line profiles that match observed features in CTTSs.

Findings

Conical-shell wind has a half opening angle of about 35 degrees.

Model reproduces narrow, low-velocity blueshifted He I (10830) absorption.

Wind contribution to hydrogen lines depends on wind temperature.

Abstract

We present the emission line profile models of hydrogen and helium based on the results from axisymmetric magnetohydrodynamics (MHD) simulations of the wind formed near the disk-magnetosphere boundary of classical T Tauri stars (CTTSs). We extend the previous outflow models of `the conical-shell wind' by Romanova et al. to include a well defined magnetospheric accretion funnel flow which is essential for modelling the optical and near-infrared hydrogen and helium lines of CTTSs. The MHD model with an intermediate mass-accretion rate shows outflows in conical-shell shape with a half opening angle about 35 degrees. The flow properties such as the maximum outflow speed in the conical-shell wind, maximum inflow speed in the accretion funnel, mass-accretion and mass-loss rates are comparable to those found in a typical CTTS. The density, velocity and modified temperature from the MHD simulations are used in a separate radiative transfer model to predict the line profiles and test the consistency of the MHD models with observations. The line profiles are computed with various combinations of X-ray luminosities, temperatures of X-ray emitting plasma, and inclination angles. A rich diversity of line profile morphology is found, and many of the model profiles are very similar to those found in observations. We find that the conical-shell wind may contribute to the emission in some hydrogen lines (e.g. H-alpha, H-beta, Pa-beta and Pa-gamma) significantly when the temperature in the wind is relatively high (e.g. \sim 10^{4} K); however, the wind contribution decreases rapidly when a lower wind temperature is adopted. The model well reproduces a relatively narrow and low-velocity blueshifted absorption component in He I (10830), which are often seen in observations.