Distortion of Magnetic Fields in a Starless Core. VI. Application of Flux Freezing Model and Core Formation of FeSt 1–457

Abstract

Observational data for the hourglass-like magnetic field toward the starless dense core FeSt 1–457 were compared with a flux freezing magnetic field model. Fitting of the observed plane-of-sky magnetic field using the flux freezing model gave a residual angle dispersion comparable to the results based on a simple 3D parabolic model. The best-fit parameters for the flux freezing model were a line-of-sight magnetic inclination angle of γ mag  = 35° ± 15° and a core center to ambient (background) density contrast of ρ c / ρ bkg  = 75. The initial density for core formation ( ρ 0 ) was estimated to be ρ c /75 = 4670 cm −3 , which is about one order of magnitude higher than the expected density (∼300 cm −3 ) for the interclump medium of the Pipe Nebula. FeSt 1–457 is likely to have been formed from the accumulation of relatively dense gas, and the relatively dense background column density of A V ≃ 5 mag supports this scenario. The initial radius (core formation radius) R 0 and the initial magnetic field strength B 0 were obtained to be 0.15 pc (1.64 R ) and 10.8–14.6 μ G, respectively. We found that the initial density ρ 0 is consistent with the mean density of the nearly critical magnetized filament with magnetic field strength B 0 and radius R 0 . The relatively dense initial condition for core formation can be naturally understood if the origin of the core is the fragmentation of magnetized filaments.