On dust entrainment in photoevaporative winds

TL;DR

This study uses advanced simulations to explore how dust grains are carried away by photoevaporative winds in protoplanetary discs, revealing size-dependent entrainment limits and dust pileup phenomena.

Contribution

It introduces a novel simulation approach with unequal-mass particles and a one-fluid model to analyze dust entrainment across a wide density and drag range in protoplanetary discs.

Findings

Only micron-sized dust grains can be entrained in EUV-driven winds.

Maximum grain size entrained is determined by dust settling, not aerodynamic drag.

Dust grains show size sorting in the outflow, with larger grains carried out at 10-20 AU.

Abstract

We investigate dust entrainment by photoevaporative winds in protoplanetary discs using dusty smoothed particle hydrodrodynamics (SPH). We use unequal-mass particles to resolve more than five orders of magnitude in disc/outflow density and a one-fluid formulation to efficiently simulate an equivalent magnitude range in drag stopping time. We find that only micron sized dust grains and smaller can be entrained in EUV driven winds. The maximum grain size is set by dust settling in the disc rather than aerodynamic drag in the wind. More generally, there is a linear relationship between the base flow density and the maximum entrainable grain size in the wind. A pileup of micron sized dust grains can occur in the upper atmosphere at critical radii in the disc as grains decouple from the low-density wind. Entrainment is a strong function of location in the disc, resulting in a size sorting of grains in the outflow---the largest grain being carried out between $10$--$20\,$AU. The peak dust density for each grain size occurs at the inner edge of its own entrainment region.