Radiation driven-dust hydrodynamics in late-phase AGB stars

Abstract

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 elusive. In this work, we broadly investigate the role of dust and radiation hydrodynamics in forming dust and gas structures, heterogeneous clumps observable in AGB remnants and planetary nebulae (PNe). Of interest in this study are the spatial perturbations driven by instabilities in the space that the mass travels through. These spatial perturbations in the dust and gas field may be responsible for forming larger clumps, such as cometary knots, seen in the PNe phase. Previous studies have considered similar physics in dust-driven winds at shorter lengths and time scales, using either 1D simulations or 2D simulations with a single mixed particle–gas fluid. Here we present an Eulerian–Lagrangian method for studying this problem at larger length and time scales. Simulations are performed in 2D, solving the Euler equations with source terms resulting from the particle phase, represented by free Lagrangian points. Radiation coupling was implemented for the particle phase, modeling radiation heating and acceleration of the particles and subsequent coupling to the gas phase through non-continuum heat and momentum transfer models. Spatial perturbations of the dust and radiation fields were found to drive the formation of small dust mass clumps that survive to late times, though these remain below the size of those observed in many PNe.