Schisano, Eugenio (2010) Characterizing circumstellar disk around young stars. [Tesi di dottorato] (Inedito)

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Abstract

The circumstellar disks play a fundamental role in star and planet formation process. Studies on circumstellar disks are generally carried on following two viable approaches: "statistical" studies, where a large samples of sources are measured to determine mean disk common properties, detailed study on individual objects can shed the light on processes, like mass accretion, central star irradiation or photoevaporation, that compete in defining the shape and the lifetime of the disks, improving the theoretical models or, hopefully, to directly catch a planet in the process of forming. Although both approaches converge toward a general scenario, they are sensitive only the disk dust component, while recently there is a strong interest on the gas, since it constitutes most of the mass of the circumstellar disks, determining the dust dynamic and the settling process, and its dispersal timescales limit the formation of gas giant planets. In this work I present a synoptic study carried on the young stellar object TCha, belonging to the class of "transition" disks, peculiar systems where very rapid evolution is ongoing. Such transitional disks are rare and, due to their classification based on the shape of the spectral energy distribution, do not represent an homogeneous class. For such reasons the characterization of any further object is extremely important to understand if we are dealing with a planetary system in formation. On the other side, I carried on a systematic study on recent discovered diagnostic for the gaseous disk component. The fine structure infrared emission line of [Ne ii] at 12.8 m has been discovered in more than 70 object. This line is thought to be produced by X-ray irradiation of the warm protoplanetary disk atmospheres, however the observational correlation between [Ne ii]luminosities and measured X-ray luminosities shows a large scatter. Such spread limits the utility of this line as a probe of the gaseous phase of disks, as several authors have suggested pollution by outflows as a probable cause of the observed scatter. For the first time with this work it has been explored the possibility that the large variations in the observed [Ne ii] luminosity may be caused instead by different star-disk parameters.

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