Dissecting the Moth: Discovery of an off-centered ring in the HD 61005 debris disk with high-resolution imaging

TL;DR

This study uses high-resolution imaging to reveal an off-centered narrow ring in the debris disk around HD 61005, suggesting potential planetary influence and complex dust scattering properties.

Contribution

First high-resolution imaging of both components of the asymmetric debris disk, revealing a narrow ring with offset and brightness asymmetries, and setting limits on planetary companions.

Findings

The debris ring is inclined at 84.3 degrees with a semi-major axis of 61.25 AU.

The ring center is offset from the star by approximately 2.75 AU.

Brightness asymmetries suggest forward-scattering grains and possible density enhancements.

Abstract

The debris disk known as "The Moth" is named after its unusually asymmetric surface brightness distribution. It is located around the ~90 Myr old G8V star HD 61005 at 34.5 pc and has previously been imaged by the HST at 1.1 and 0.6 microns. Polarimetric observations suggested that the circumstellar material consists of two distinct components, a nearly edge-on disk or ring, and a swept-back feature, the result of interaction with the interstellar medium. We resolve both components at unprecedented resolution with VLT/NACO H-band imaging. Using optimized angular differential imaging techniques to remove the light of the star, we reveal the disk component as a distinct narrow ring at inclination i=84.3 \pm 1.0{\deg}. We determine a semi-major axis of a=61.25 \pm 0.85 AU and an eccentricity of e=0.045 \pm 0.015, assuming that periastron is located along the apparent disk major axis. Therefore, the ring center is offset from the star by at least 2.75 \pm 0.85 AU. The offset, together with a relatively steep inner rim, could indicate a planetary companion that perturbs the remnant planetesimal belt. From our imaging data we set upper mass limits for companions that exclude any object above the deuterium-burning limit for separations down to 0.3". The ring shows a strong brightness asymmetry along both the major and minor axis. A brighter front side could indicate forward-scattering grains, while the brightness difference between the NE and SW components can be only partly explained by the ring center offset, suggesting additional density enhancements on one side of the ring. The swept-back component appears as two streamers originating near the NE and SW edges of the debris ring.