Radiation-Driven Dust Hydrodynamics in late-phase AGB stars

The interplay of stellar luminosity variations and dust hydrodynamics in Asymptotic Giant Branch (AGB) stars, and the consequences for dust survival and mass-loss remain mysterious. In this work, we broadly investigate the role of dust and radiation in the formation of hydrodynamic features, known as cometary knots, observable in planetary nebulae (PNe), post AGB remnants. Luminosity variations arise due to turbulent thermal convection and manifest as granules, observable in the photosphere of stars, such as our own. Scaling laws suggest a size and energy for granules in AGB stars, far larger than those observed on our own sun. These intensity perturbations are one possible source for the formation of hydrodynamic features in PNe. Previous research studies have considered similar physics in dust-driven winds at shorter length and time scales, using either 1D simulations, or 2D simulations with a single mixed particle-gas fluid. Here we present a Eulerian-Lagrangian method for studying this problem at larger length and time scales. Simulations are performed using the FLASH code, in part developed by the Flash Center at the University of Chicago. The Particle-in-Cell method was used with the two-dimensional Euler equations and solved using the directionally split piecewise-parabolic method (PPM). This method was then modified for the astrophysics regime by implementing radiation and non-continuum drag models for the particle and gas phases. The effects of a perturbed radiation field due to strong turbulent eddies of granulation have been investigated to determine if these could be responsible for the formation of cometary knots observed in planetary nebulae.