HD 104860 and HD 192758: two debris disks newly imaged in scattered-light with HST

TL;DR

This study presents the first scattered-light images of two debris disks around stars HD 104860 and HD 192758, revealing their structure, composition, and potential differences from brighter disks, using archival HST data.

Contribution

First imaging of these debris disks in scattered light, providing detailed morphology and composition insights, and suggesting a broader population of low-albedo debris disks.

Findings

Disks are at ~114 au and ~95 au with inclinations ~58° and ~59°.

Disks have low scattering albedos of 10% and 13%.

Disks differ from brighter, higher-albedo disks, indicating different compositions or formation processes.

Abstract

We present the first scattered-light images of two debris disks around the F8 star HD 104860 and the F0V star HD 192758, respectively $\sim45$ and $\sim67$ pc away. We detected these systems in the F110W and F160W filters through our re-analysis of archival Hubble Space Telescope NICMOS data with modern starlight subtraction techniques. Our image of HD 104860 confirms the morphology previously observed by Herschel in thermal emission with a well-defined ring at radius $\sim114$ au inclined $\sim58$ degrees. Although the outer edge profile is consistent with dynamical evolution models, the sharp inner edge suggests sculpting by unseen perturbers. Our images of HD 192758 reveal a disk at radius $\sim95$ au inclined by $\sim59$ degrees, never resolved so far. These disks have low scattering albedos of 10% and 13% respectively, inconsistent with water ice grain compositions. They are reminiscent of several other disks with similar inclination and scattering albedos: Fomalhaut, HD 92945, HD 202628, and HD 207129. They are also very distinct from brighter disks in the same inclination bin, which point to different compositions between these two populations. Varying scattering albedo values can be explained by different grain porosities, chemical compositions, or grain size distributions, which may indicate distinct formation mechanisms or dynamical processes at work in these systems. Finally, these faint disks with large infrared excesses may be representative of an underlying population of systems with low albedo values. Searches with more sensitive instruments on HST or on the James Webb Space Telescope and using state-of-the art starlight-subtraction methods may help discover more of such faint systems.