Mid-Infrared Spectrum of the Disk around the Forming Companion GQ Lup B Revealed by JWST/MIRI

TL;DR

This study uses JWST/MIRI mid-infrared spectroscopy to analyze the disk around the forming brown dwarf GQ Lup B, revealing grain growth and potential disk structure features crucial for understanding planetary formation.

Contribution

First MIR spectroscopic observations of GQ Lup B's disk with high-contrast imaging, demonstrating the potential of JWST/MIRI for studying circumplanetary disks around forming companions.

Findings

No silicate feature detected, indicating grain growth and dust settling.

Possible presence of an inner cavity larger than sublimation radius.

Disk may be very compact or have a large inner cavity, requiring further observations.

Abstract

GQ Lup B is a forming brown dwarf companion ($M\sim10-30~M_J$) showing evidence for an infrared excess associated with a disk surronding the companion itself. Here we present mid-infrared (MIR) observations of GQ Lup B with the Medium Resolution Spectrograph (MRS) on JWST, spanning $4.8-11.7~\mu$m. We remove the stellar contamination using reference differential imaging based on principal component analysis (PCA), demonstrating that the MRS can perform high-contrast science. Our observations provide a sensitive probe of the disk surrounding GQ Lup B. We find no sign of a silicate feature, similar to other disk surrounding very low mass objects, which likely implies significant grain growth ($a_{\mathrm{min}}\gtrsim5~\mu$m), and potentially dust settling. Additionally, we find that if the emission is dominated by an inner wall, the disk around the companion might have an inner cavity larger than the one set by sublimation. Conversely, if our data probe the emission from a thin flat disk, we find the disk to be very compact. More observations are required to confirm this finding and assess the vertical structure of the disk. This approach paves the path to the future study of circumplanetary disks and their physical properties. Our results demonstrate that MIR spectroscopic observations can reveal the physical characteristics of disks around forming companions, providing unique insights into the formation of giant planets, brown dwarfs and their satellites.