Influence of Drag Forces and Interstellar Magnetic Fields on Radiation Driven Dust Arcs Around Runaway Stars

Abstract

Peculiarities of the interstellar dust distribution around runaway stars have been modeled in the frame of the cold gas model with the Lagrangian approach. Interstellar dust (ISD) particles move with respect to the star due to the relative motion of the star and interstellar gas. The stellar radiation pressure changes the trajectories of the particles forming a dust void cavity behind the star. The shape of the boundary of the cavity is parabolic. In addition to the radiation pressure force, ISD may suffer drug force due to interaction with protons and electrons and electromagnetic force. The effects of these forces are explored in the paper. We found that drag force pulls the cavity boundary closer to the star in the apex region and straightens the tail region into a cylindrical shape. We also found that the caustic structure in this case consists of multiple folds. On the other hand, the influence of the interstellar magnetic field depends on its orientation. We considered magnetic fields parallel and perpendicular to interstellar medium velocity. Under the influence of the magnetic field dust particles can penetrate void region due to gyration. In the presence of parallel magnetic field trajectories form a swallowtail caustics and dust arc is bounded. The effect of the perpendicular magnetic field is more complex, trajectories form cusp caustics and wave-shaped pattern in the tail region.