Photophoretic Structuring of Circumstellar Dust Disks

TL;DR

This paper investigates how photophoresis influences dust distribution in circumstellar disks, revealing that it causes particles smaller than 10 cm to migrate outward, forming distinct inner holes and outer disks depending on particle size and gas density.

Contribution

It introduces a detailed model of dust accumulation by photophoresis in optically thin gas disks, highlighting the formation of inner holes and outer disks with size-dependent features.

Findings

Photophoresis pushes particles <10 cm outward to 0.1-100 AU.

Inner hole radius depends on gas mean free path and dust properties.

Outer disk particle sizes are larger than in gas-free models.

Abstract

We study dust accumulation by photophoresis in optically thin gas disks. Using formulae of the photophoretic force that are applicable for the free molecular regime and for the slip-flow regime, we calculate dust accumulation distances as a function of the particle size. It is found that photophoresis pushes particles (smaller than 10 cm) outward. For a Sun-like star, these particles are transported to 0.1-100 AU, depending on the particle size, and forms an inner disk. Radiation pressure pushes out small particles (< 1 mm) further and forms an extended outer disk. Consequently, an inner hole opens inside ~0.1 AU. The radius of the inner hole is determined by the condition that the mean free path of the gas molecules equals the maximum size of the particles that photophoresis effectively works on (100 micron - 10 cm, depending on the dust property). The dust disk structure formed by photophoresis can be distinguished from the structure of gas-free dust disk models, because the particle sizes of the outer disks are larger, and the inner hole radius depends on the gas density.