2020ApJ...888..120K

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 (ρ₀) 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) R₀ and the initial magnetic field strength B₀ were obtained to be 0.15 pc (1.64R) and 10.8-14.6 µG, respectively. We found that the initial density ρ₀ is consistent with the mean density of the nearly critical magnetized filament with magnetic field strength B₀ and radius R₀. The relatively dense initial condition for core formation can be naturally understood if the origin of the core is the fragmentation of magnetized filaments.