Bow shocks, bow waves, and dust waves – II. Beyond the rip point

• Published in: Monthly notices of the Royal Astronomical Society 2019-07, Vol.486 (3), p.4423-4442
• Main Authors: Henney, William J, Arthur, S J
• Format: Article
• Language: English
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stz1130

ABSTRACT Dust waves are a result of gas–grain decoupling in a stream of dusty plasma that flows past a luminous star. The radiation field is sufficiently strong to overcome the collisional coupling between grains and gas at a rip point, where the ratio of radiation pressure to gas pressure exceeds a critical value of roughly 1000. When the rip point occurs outside the hydrodynamic bow shock, a separate dust wave may form, decoupled from the gas shell, which can either be drag-confined or inertia-confined, depending on the stream density and relative velocity. In the drag-confined case, there is a minimum stream velocity of roughly 60 km s−1 that allows a steady-state stagnant drift solution for the dust wave apex. For lower relative velocities, the dust dynamics close to the axis exhibit a limit cycle behaviour (rip and snap back) between two different radii. Strong coupling of charged grains to the plasma’s magnetic field can modify these effects, but for a quasi-parallel field orientation the results are qualitatively similar to the non-magnetic case. For a quasi-perpendicular field, on the other hand, the formation of a decoupled dust wave is strongly suppressed.