2006/04/26 by Akira Mizuta, J. Kane, Jave O. Kane +7 · 4 citations
Physics and Astronomy · #Amplitude #Astrophysics and Star Formation Studies #Atomic and Molecular Physics #Atomic physics #Instability #Laser-Plasma Interactions and Diagnostics #Mechanics #Molecular physics #Optics #Perturbation (astronomy) #Physics #Quantum mechanics #Wavelength #astro-ph
paper · pdf · doi:10.1086/505458
published as Astrophys.J. 647 (2006) 1151-1158 · 21 pages, 8 figures, accepted for publication in ApJ. high resolution figures available upon request
arxiv created 2006/04/26 · openalex publication_date 2006/08/15 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We investigate numerically the hydrodynamic instability of an ionization front (IF) accelerating into a molecular cloud, with imposed initial perturbations of different amplitudes. When the initial amplitude is small, the imposed perturbation is completely stabilized and does not grow. When the initial perturbation amplitude is large enough, roughly, the ratio of the initial amplitude to wavelength is greater than 0.02, portions of the IF temporarily separate from the molecular cloud surface, locally decreasing the ablation pressure. This causes the appearance of a large, warm H I region and triggers nonlinear dynamics of the IF. The local difference of the ablation pressure and acceleration enhances the appearance and growth of a multimode perturbation. The stabilization usually seen at the IF in the linear regime does not work due to the mismatch of the modes of the perturbations at the cloud surface and of the density in the H II region above the cloud surface. Molecular pillars are observed in the late stages of the large amplitude perturbation case. The velocity gradient in the pillars is in reasonably good agreement with that observed in the Eagle Nebula. The initial perturbation is imposed in three different ways: in density, in incident photon number flux, and in the surface shape. All cases show both stabilization for a small initial perturbation and large growth of the second harmonic by increasing amplitude of the initial perturbation above a critical value.