Triggered star formation in Bright-Rimmed Clouds: The Eagle Nebula revisited

摘要

A three dimensional Smoothed Particle Hydrodynamical (SPH) model has beenextended to study the radiative driven implosion effect of massive stars on thedynamical evolutions of surrounding molecular clouds. The new elements in theupgraded code are the inclusion of Lyman continuum in the incident radiationflux and the treatment of hydrogen ionisation process; introducing ionisationheating & recombination cooling effects; and adding a proper description of themagnetic and turbulent pressures to the internal pressure of the molecularcloud. The application of this newly developed model to the structure of themiddle Eagle Nebula finger suggests that the shock induced by the ionisingradiation at the front side of the head precedes an ionisation front movingtowards the center of the core, and that the core at the fingertip is attransition stage evolving toward a state of induced star formation. Thedynamical evolution of the velocity field of the simulated cloud structure isdiscussed to illustrate the role of the self-gravity and the different cloudmorphologies which appear at different stages in the evolutionary process ofthe cloud. The modelled gas evaporation rate is consistent with that of currentother models and the density, temperature and chemical profiles are agreementwith the observed values. The relative lifetimes of different simulated cloudmorphologies suggests a possible answer to the question of why morebright-rimmed clouds are observed to possess a flat-core than an elongated-coremorphology. [Abridged]