By Bernd Sturmfels
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2004b) studied the possibility that X-rays from the central star heat the disk surface. In comparison to UV radiation, the X-ray emission from T Tauri stars is well known from observations. They used a simple two-dimensional model in order to derive an upper limit for the mass-loss rate and find a lower mass-loss rate than in the case of UV radiation. In the presence of a significant UV field, X-ray driven disk winds seem to be unlikely to play a significant role in the evolution of disk winds around low-mass stars.
EUV- and FUV-dominated flows. For the case of O stars, EUV-dominated flows occur close to the star, whereas FUV-dominated flows tend to apply for moderate-sized (rg < rd < 100 AU) photoevaporating disks at larger distances. In the case of FUV-dominated flows, the neutral flow launches supersonically from the disk surface, passes a shock front behind which it slows down and becomes subsonic. The subsonic region extends up to the ionization front. From there the ionized flow is able to escape supersonically again (see also Fig.
The natural way to produce dust in a debris disk is by collisions between planetesimals (Weissman, 1984), not unlike those occurring in the asteroid and Kuiper-Belt objects. , 2005) shows that many systems have a similar structure to that of the Solar System. The presence of a planet can influence and shape the structure of the debris disk (Kenyon and Bromley, 2004a, b). By determining the location and rate of dust production, constraints can be placed upon the dynamics of the planetesimal disk and the presence and influence of planets could be inferred.
