Three-Dimensional Simulations of Rotationally-Induced Line Variability from a Classical T Tauri Star

Ryuichi Kurosawa, Marina M. Romanova & Tim J. Harries, 2008, MNRAS, in press

[ Top ] [ Preprint ] [ Movies ]

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). We find the line profiles are relatively insensitive to the details of the temperature structure of accretion funnels, but are influenced more by the mean temperature of the flow and its geometry. 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.

↑

Preprint

Download PDF Version

↑

Model Summary

Click on AVI movie to see moves. Click on Summary Plot to see summary plots.

Basic Model parameters: R=1.8Rsun, M=0.8Msun, T(photosphere)=4000K, T(hot spot averaged)=8000K, Mdot(accretion)~2x10^8 Msun/yr

Basic Model Configuration:

[IMAGE]

Dependency on inclination angle (i) and tilt angle (Theta)

With temperature structure of Romanova et al (2004).

i	Theta	gamma	Plots
10	15	1.1	Pa-beta: [AVI movie] [Summary Plot] [Density Plot] [Temperature Plot]
60	15	1.1	Pa-beta: [AVI movie] [Summary Plot] [Density Plot] [Temperature Plot] Br-gamma: [AVI movie] [Summary Plot] H-beta: [AVI movie] [Summary Plot]
80	15	1.1	Pa-beta: [AVI movie] [Summary Plot] [Density Plot] [Temperature Plot]
60	60	1.1	Pa-beta: [AVI movie] [Summary Plot] [Density Plot] [Temperature Plot]
60	90	1.1	Pa-beta: [AVI movie] [Summary Plot] [Density Plot] [Temperature Plot]

No mis-alingment Case (Theta=0) (Experimental)

With i =60 deg. :

Temperature Law	Plots
Hartmann	Pa-beta: [AVI movie] [ Summary Plot]
Romanova	Pa-beta: [AVI movie] [ Summary Plot]

SU Aur models (Experimental)

With Romanova's Temperature structure and i =80 deg.
Density is same as for Theta=60 and 90 case above, but scaled up for higher mass accreation rate.

Theta	Plots
90	Pa-beta: [AVI movie] [Summary Plot] H-beta: [AVI movie] [Summary Plot]
60	Pa-beta: [AVI movie] [Summary Plot] H-beta: [AVI movie] [Summary Plot]

↑