The perturbed sublimation rim of the dust disk around the post-AGB binary IRAS08544-4431

TL;DR

This study models the inner rim of a circumbinary disk around a post-AGB star using radiative transfer, revealing a dust sublimation-driven structure with asymmetries likely caused by binary interactions.

Contribution

It provides the first detailed radiative transfer model of the inner disk rim around IRAS08544-4431, incorporating dust settling and hydrostatic equilibrium, and highlights unresolved flux and asymmetries.

Findings

Inner rim starts at 8.25 au and is rounded.

Model matches spectral energy distribution and interferometric data.

Asymmetries likely caused by disk-binary interactions.

Abstract

Context: Post-Asymptotic Giant Branch (AGB) binaries are surrounded by stable dusty and gaseous disks similar to the ones around young stellar objects. Whereas significant effort is spent on modeling observations of disks around young stellar objects, the disks around post-AGB binaries receive significantly less attention, even though they pose significant constraints on theories of disk physics and binary evolution. Aims: We want to examine the structure of and phenomena at play in circumbinary disks around post-AGB stars. We continue the analysis of our near-infrared interferometric image of the inner rim of the circumbinary disk around IRAS08544-4431. We want to understand the physics governing this inner disk rim. Methods: We use a radiative transfer model of a dusty disk to reproduce simultaneously the photometry as well as the near-infrared interferometric dataset on IRAS08544-4431. The model assumes hydrostatic equilibrium and takes dust settling self-consistently into account. Results: The best-fit radiative transfer model shows excellent agreement with the spectral energy distribution up to mm wavelengths as well as with the PIONIER visibility data. It requires a rounded inner rim structure, starting at a radius of 8.25 au. However, the model does not fully reproduce the detected over-resolved flux nor the azimuthal flux distribution of the inner rim. While the asymmetric inner disk rim structure is likely to be the consequence of disk-binary interactions, the origin of the additional over-resolved flux remains unclear. Conclusions: As in young stellar objects, the disk inner rim of IRAS08544-4431 is ruled by dust sublimation physics. Additional observations are needed to understand the origin of the extended flux and the azimuthal perturbation at the inner rim of the disk.