Line and continuum radiative transfer modelling of AA Tau

TL;DR

This study models the photometric and spectroscopic variability of AA Tau using radiative transfer simulations to understand its disc warp, magnetosphere, and outflow characteristics.

Contribution

It provides the first comprehensive radiative transfer model of AA Tau's disc, magnetosphere, and outflow, constraining key physical parameters from observations.

Findings

Best-fit mass accretion rate of 5×10⁻⁹ M☉/yr

Magnetosphere truncates disc between 5.2 and 8.8 R★

Disc wind temperature around 8000 K

Abstract

We present photometric and spectroscopic models of the Classical T Tauri star AA Tau. Photometric and spectroscopic variability present in observations of AA Tau is attributed to a magnetically induced warp in the accretion disc, periodically occulting the photosphere on an 8.2--day timescale. Emission line profiles show signatures of both infall, attributed to magnetospherically accreting material, and outflow. Using the radiative transfer code TORUS, we have investigated the geometry and kinematics of AA Tau's circumstellar disc and outflow, which is modelled here as a disc wind. Photometric models have been used to constrain the aspect ratio of the disc, the offset angle of the magnetosphere dipole with respect to the stellar rotation axis, and the inner radius of the circumstellar disc. Spectroscopic models have been used to constrain the wind and magnetosphere temperatures, wind acceleration parameter, and mass loss rate. We find observations are best fitted by models with a mass accretion rate of $5\times10^{-9}$ M$_\odot$ yr$^{-1}$, a dipole offset of between $10^\circ$ and $20^\circ$, a magnetosphere that truncates the disc from 5.2 to 8.8 R$_\star$, a mass-loss-rate to accretion-rate ratio of ~ 0.1, a magnetosphere temperature of 8500 -- 9000 K, and a disc wind temperature of 8000 K.