Discovery of variable X-ray absorption in the cTTS AA Tauri

Abstract

We present XMM-Newton X-ray and UV observations of the classical T Tauri star AA Tau covering almost two rotational periods where $P_{\rm rot} \sim$ 8.5 days. Clear, but uncorrelated variability is found at both wavebands. The variability observed at ~2100 A follows the previously known optical period. Spectral analysis of the X-ray data results in significant variability in the X-ray absorption such that the times of maximal X-ray absorption and UV extinction coincide. Placing the coronal emission in regions at low up to moderate magnetic latitudes and attribution of the variable X-ray absorption to accretion curtains and/or the disk warp provides a consistent physical picture. However, the derived X-ray absorption and optical extinction at times of maximal optical/UV brightness, i.e. outside occultation, are difficult to reconcile, requiring additional absorption in a disk wind or a peculiar dust grain distribution.