Apocenter glow in eccentric debris disks: implications for Fomalhaut and epsilon Eridani

TL;DR

This paper investigates the phenomenon of apocenter glow in eccentric debris disks, showing it can be brighter at long wavelengths and offering a new way to analyze dust properties in disks like Fomalhaut and epsilon Eridani.

Contribution

The study introduces models of apocenter glow at long wavelengths, providing a new interpretation of existing observations to constrain dust grain properties in debris disks.

Findings

Apocenter glow is brighter than pericenter at long wavelengths in eccentric disks.

Existing far-infrared and millimeter images can be reinterpreted as evidence of apocenter glow.

Reinterpretation constrains dust grain sizes and compositions in debris disks.

Abstract

Debris disks often take the form of eccentric rings with azimuthal asymmetries in surface brightness. Such disks are often described as showing "pericenter glow", an enhancement of the disk brightness in regions nearest the central star. At long wavelengths, however, the disk apocenters should appear brighter than their pericenters: in the long wavelength limit, we find the apocenter/pericenter flux ratio scales as 1+e for disk eccentricity e. We produce new models of this "apocenter glow" to explore its causes and wavelength dependence and study its potential as a probe of dust grain properties. Based on our models, we argue that several far-infrared and (sub)millimeter images of the Fomalhaut and epsilon Eridani debris rings obtained with Herschel, JCMT, SHARC II, ALMA, and ATCA should be reinterpreted as suggestions or examples of apocenter glow. This reinterpretation yields new constraints on the disks' dust grain properties and size distributions.