2001/04/03 by W. Steffen, J. A. López, J. A. Lopez +2
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Bow shock (aerodynamics) #Circular symmetry #Classical mechanics #Mechanics #Physics #Planetary nebula #Shock (circulatory) #Shock wave #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/321592
accepted for publication in The Astrophysical Journal
arxiv created 2001/04/03 · openalex publication_date 2001/08/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present an alternative model for the formation of fast low-ionization emission regions (FLIERs) in planetary nebulae that is able to account for many of their attendant characteristics and to circumvent the problems of the collimation/formation mechanisms found in previous studies. In this model, the section of the stellar wind flowing along the symmetry axis carries less mechanical momentum than that at higher latitudes and temporarily develops a concave or inverted shock geometry. The shocked ambient material is thus refracted toward the symmetry axis, instead of away from it, and accumulates in the concave section. The reverse is true for the outflowing stellar wind, which in the reverse shock is refracted away from the axis. It surrounds the stagnation region of the bow shock and confines the trapped ambient gas. The latter has time to cool and is then compressed into a dense "stagnation knot" or "stagnation jet." In the presence of a variable stellar wind these features may eventually overrun the expanding nebular shell and appear as detached FLIERs. We present representative two- and three-dimensional hydrodynamic simulations of the formation and early evolution of stagnation knots and jets and compare their dynamical properties with those of FLIERs in planetary nebulae.