Photoionization of cool MHD diskwinds - On the source of the far UV emission lines from T Tauri stars

Abstract

Recent ultraviolet observations point out that there is hot, dense plasma associated with the optical jet in some T Tauri stars. In this contribution, cool MHD disk wind physics is reviewed by means of a self-similar analytical model to analyze whether hot (Te similar or equal to 80, 000 K) and dense (n(e) similar or equal to 10(9) cm(-3)) plasma can be produced in disk winds. It is shown that these high densities can only be achieved at the base of the wind where the stellar X-rays radiation field is strong. The propagation of the X-rays radiation through the disk wind is analyzed: a cocoon of photoionized gas is generated around the star. However, it is difficult to foresee how temperatures as high as similar to5 x 10(4) can be reached unless a significant fraction of the X-rays radiation is produced by magnetic reconnection at the boundary between the stellar magnetosphere and the accretion disk.