Revealing the fastest component of the DG Tauri outflow through X-rays

Abstract

Context: Some T Tauri stars show a peculiar X-ray spectrum that can be modelled by two components with different absorbing column densities.
Aims: We seek to explain the soft X-ray component in DG Tau, the best studied of these sources, with an outflow model, taking observations at other wavelengths into consideration.
Methods: We constrain the outflow properties through spectral fitting and employ simple semi-analytical formulae to describe properties of a shock wave that heats up the X-ray emitting region.
Results: The X-ray emission is consistent with its arising from the fastest and innermost component of the optically detected outflow. Only a small fraction of the total mass loss is required for this X-ray emitting component. Our favoured model requires shock velocities between 400 and 500 km s^-1. For a density >10⁵ cm^-3 all dimensions of the shock cooling zone are only a few AU, so even in optical observations this cannot be resolved.
Conclusions: This X-ray emission mechanism in outflows may also operate in other, less absorbed T Tauri stars, in addition to corona and accretion spots.