Gemini Planet Imager Observations of a Resolved Low-Inclination Debris Disk Around HD 156623

TL;DR

This paper presents high-resolution polarimetric imaging and modeling of the debris disk around HD 156623, revealing its unique morphology, inner radius constraints, and implications for dust grain retention influenced by gas drag.

Contribution

It provides the first resolved scattered light image of HD 156623's debris disk, constrains its inner radius, and measures the polarized scattering phase function, highlighting its unique features among low-inclination disks.

Findings

Disk lacks a visible inner clearing.

Inner radius constrained to less than 26.6 AU (scattered light) and 13.4 AU (SED).

Gas drag may influence dust grain retention.

Abstract

The 16 Myr-old A0V star HD 156623 in the Scorpius--Centaurus association hosts a high-fractional-luminosity debris disk, recently resolved in scattered light for the first time by the Gemini Planet Imager (GPI) in polarized intensity. We present new analysis of the GPI H-band polarimetric detection of the HD 156623 debris disk, with particular interest in its unique morphology. This debris disk lacks a visible inner clearing, unlike the majority of low-inclination disks in the GPI sample and in Sco-Cen, and it is known to contain CO gas, positioning it as a candidate ``hybrid'' or ``shielded'' disk. We use radiative transfer models to constrain the geometric parameters of the disk based on scattered light data and thermal models to constrain the unresolved inner radius based on the system's spectral energy distribution (SED). We also compute a measurement of the polarized scattering phase function, adding to the existing sample of empirical phase function measurements. We find that HD 156623's debris disk inner radius is constrained to less than 26.6 AU from scattered light imagery and less than 13.4 AU from SED modeling at a 99.7% confidence interval, and suggest that gas drag may play a role in retaining sub-blowout size dust grains so close to the star.