Three-dimensional simulations of rotationally-induced line variability from a Classical T Tauri star with a misaligned magnetic dipole

TL;DR

This study uses 3-D MHD simulations to model line variability in classical T Tauri stars caused by rotational effects and magnetic misalignment, matching observed hydrogen line profiles.

Contribution

It introduces a comprehensive 3-D simulation framework linking magnetic geometry to observable line variability in CTTS.

Findings

Models with small magnetic misalignment angles fit observations better.

Line variability shows anti-correlation in blue and red wings for certain viewing angles.

Good agreement between simulated and observed hydrogen line profiles.

Abstract

We present three-dimensional (3-D) simulations of rotationally induced line variability arising from complex circumstellar environment of classical T Tauri stars (CTTS) using the results of the 3-D magnetohydrodynamic (MHD) simulations of Romanova et al., who considered accretion onto a CTTS with a misaligned dipole magnetic axis with respect to the rotational axis. The density, velocity and temperature structures of the MHD simulations are mapped on to the radiative transfer grid, and corresponding line source function and the observed profiles of neutral hydrogen lines (H-beta, Pa-beta and Br-gamma) are computed using the Sobolev escape probability method. We study the dependency of line variability on inclination angles (i) and magnetic axis misalignment angles (Theta). By comparing our models with the Pa-beta profiles of 42 CTTS observed by Folha & Emerson, we find that models with a smaller misaligngment angle (Theta<~15 deg.) are more consistent with the observations which show that majority of Pa-beta are rather symmetric around the line centre. For a high inclination system with a small dipole misalignment angle (Theta ~ 15 deg.), only one accretion funnel (on the upper hemisphere) is visible to an observer at any given rotational phase. This can cause an anti-correlation of the line equivalent width in the blue wing (v<0) and that in the red wing (v>0) over a half of a rotational period, and a positive correlation over other half. We find a good overall agreement of the line variability behaviour predicted by our model and those from observations. (Abridged)