Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21831202g&link_type=abstract
American Astronomical Society, AAS Meeting #218, #312.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
Class II Pre-Main Sequence stars are characterized by the presence of the circumstellar disk in the equatorial plane, which is the site of the planets formation. The induced photoevaporation of disks is one of the key processes leading the evolution of these structures. Photoevaporation occurs when the disk is irradiated by UV and X-ray radiation: Far UltraViolet (FUV) photons (with energy ranging from 6eV to 13.6eV) dissociate H2 molecules, while Extreme UltraViolet (EUV, from 13.6eV to 100eV ) and X-ray photons ionize gas atoms. Since both processes heat the gas up to 1000K-10000K, the thermal pressure drives a photoevaporative flow of gas away from the disk. Photoevaporation is usually induced by the central star itself; however, direct images (taken with the Hubble Space Telescope) of the young stars surrounded by photoevaporating disks in the Orion Nebula Cluster showed that photoevaporation can be induced by the energetic radiation emitted by nearby massive stars. In these cases, the externally induced photoevaporation can dissipate the disks in short timescale (even smaller than 1 Myear in the more extreme situations). Besides, recent studies of the massive young clusters NGC2244 and NGC6611 confirmed that the evolution of circumstellar disks is affected by induced photoevaporation in the core of such massive clusters, but there is still some controversy about these results. In this talk I will review the main features of the photoevaporation process, its effects on disks evolution when it is induced by nearby ionizing sources, and the supporting observational evidences.
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