# An Exo-Kuiper Belt and An Extended Halo around HD 191089 in Scattered Light

## TL;DR

This study presents detailed scattered light imaging of the HD 191089 debris disk, revealing a Kuiper Belt-like ring and an extended, bluer halo, with analysis of dust scattering properties and modeling challenges.

## Contribution

It provides high-resolution images of the debris disk's structure and investigates dust scattering, highlighting the need for more complex models for accurate interpretation.

## Key findings

- The debris disk has a Kuiper Belt-like ring at ~46 au and a halo extending to ~640 au.
- The halo is bluer and exhibits more forward- and backward-scattering than the ring.
- Radiative transfer modeling shows inconsistencies, suggesting more realistic dust models are required.

## Abstract

We have obtained Hubble Space Telescope STIS and NICMOS, and Gemini/GPI scattered light images of the HD 191089 debris disk. We identify two spatial components: a ring resembling Kuiper Belt in radial extent (FWHM: ${\sim}$25 au, centered at ${\sim}$46 au), and a halo extending to ${\sim}$640 au. We find that the halo is significantly bluer than the ring, consistent with the scenario that the ring serves as the "birth ring" for the smaller dust in the halo. We measure the scattering phase functions in the 30{\deg}-150{\deg} scattering angle range and find the halo dust is both more forward- and backward-scattering than the ring dust. We measure a surface density power law index of -0.68${\pm}$0.04 for the halo, which indicates the slow-down of the radial outward motion of the dust. Using radiative transfer modeling, we attempt to simultaneously reproduce the (visible) total and (near-infrared) polarized intensity images of the birth ring. Our modeling leads to mutually inconsistent results, indicating that more complex models, such as the inclusion of more realistic aggregate particles, are needed.