Asymmetric Heating of the HR 4796A Dust Ring Due to Pericenter Glow

TL;DR

This study presents new mid-infrared images of the HR 4796A dust ring, confirming brightness and temperature asymmetries caused by pericenter glow due to gravitational perturbations, and models these features with specific dust properties and eccentricity.

Contribution

It provides the first resolved mid-IR images confirming pericenter glow asymmetries and models the dust ring's offset and properties to explain observed brightness variations.

Findings

Brightness and temperature asymmetries confirmed in mid-IR images.

Models with 2-micron silicate dust and eccentricity of 0.06 fit observations.

Thermal-emission parameters also explain shorter-wavelength asymmetries.

Abstract

We have obtained new resolved images of the well-studied HR 4796A dust ring at 18 and 25 microns with the 8-meter Gemini telescopes. These images confirm the previously observed spatial extent seen in mid-IR, near-IR, and optical images of the source. We detect brightness and temperature asymmetries such that dust on the NE side is both brighter and warmer than dust in the SW. We show that models of so-called pericenter glow account for these asymmetries, thus both confirming and extending our previous analyses. In this scenario, the center of the dust ring is offset from the star due to gravitational perturbations of a body with an eccentric orbit that has induced a forced eccentricity on the dust particle orbits. Models with 2-micron silicate dust particles and a forced eccentricity of 0.06 simultaneously fit the observations at both wavelengths. We also show that parameters used to characterize the thermal-emission properties of the disk can also account for the disk asymmetry observed in shorter-wavelength scattered-light images.