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 Title: 

            Gas Physics and Chemistry in transition phase disks around M, G, and A-type stars

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 Authors:

          Inga Kamp, STScI

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 Abstract:

          One of the key questions in protoplanetary disk evolution is that of the gas mass of the disk as a function of time.Young disks are easily detected in CO and various other tracers, which allows an independent assess of the gas mass. Older disks are more difficult to detect, because of their lower masses and their difference in chemical gas tracers.  In the transition phase between optically thick protoplanetray disks and debris disks (10-70 Myr), the stellar radiation field dominates the energy balance of the disk and drives its gas chemistry. Realistic stellar radiation fields of various spectral types (M through A) and their impact on the gas temperature and chemistry are discussed (X-rays/UV). In addition, the impact of dust dynamics (e.g. radiation pressure and PR effect) on the gas temperature is illustrated. Finally some conclusions for present/further observations of targets such as Beta Pictoris and AU Mic are drawn. 

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