| Description |
Protoplanetary gas and dust disks around T Tauri stars are the most importantelements in the process of planet formation. In particular, the dissipation timescale of disks sets a critical time limit for planet formation. The mechanismsof disk dissipation are poorly understood, however. Apart from the planet formationprocess itself, photoevaporation and disk instabilities induced by the magneto-rotational instability are key candidates. In both cases, heating and ionisation by stellar short-wavelength radiation plays a crucial role. High-energy stellar radiation (X-rays, extreme ultraviolet) also drives chemical networks in circumstellardisks, forming key molecules that eventually become important for the formationof life in habitable zones. However, there is little information on the X-ray radiationspectrum impinging on the disk, given various sources of photoelectric absorption.We will study disk ionisation and X-ray driven chemistry by observing X-ray sensitive lines in an outstanding and unique sample of three classical T Tauri stars in which X-rays appear to be blocked before reaching the disk. We will compare the results with a control sample of disks that appear to be irradiated by high levels of stellar X-ray radiation. Our X-ray sensitive lines include transitions from HCN, HCO+, and ortho-NH3. The interpretation of our results will be basedon thermo-chemical codes developed in the proposing team. |
