Inner edges of compact debris disks around metal-rich white dwarfs

TL;DR

This study investigates the inner edges of debris disks around metal-rich white dwarfs, revealing that high metal vapor pressure allows particles to survive closer to the star than previously thought, due to a superheated rim structure.

Contribution

The paper introduces a model explaining the survival of particles near white dwarfs by considering high vapor pressure effects and rim shielding, aligning with observations.

Findings

Inner disk edges feature superheated rims at 2500-3500 K.

Particles of olivine-sized (0.03-30 cm) can survive close to the WD.

Model matches observed disk structures when particles are Si-rich.

Abstract

A number of metal-rich white dwarfs (WDs) are known to host compact, dense particle disks, which are thought to be responsible for metal pollution of these stars. In many such systems the inner radii of disks inferred from their spectra are so close to the WD that particles directly exposed to starlight must be heated above 1500 K and are expected to be unstable against sublimation. To reconcile this expectation with observations we explore particle sublimation in H-poor debris disks around WDs. We show that because of the high metal vapor pressure the characteristic sublimation temperature in these disks is 300-400 K higher than in their protoplanetary analogues, allowing particles to survive at higher temperatures. We then look at the structure of the inner edges of debris disks and show that they should generically feature superheated inner rims directly exposed to starlight with temperatures reaching 2500-3500 K. Particles migrating through the rim towards the WD (and rapidly sublimating) shield the disk behind them from strong stellar heating, making the survival of solids possible close to the WD. Our model agrees well with observations of WD+disk systems provided that disk particles are composed of Si-rich material such as olivine, and have sizes in the range ~(0.03-30) cm.