A JWST MIRI MRS View of the $\eta$ Tel Debris Disk and its Brown Dwarf Companion

TL;DR

This study uses JWST MIRI MRS observations to analyze the $eta$ Pictoris moving group member $ au$ Tel, revealing a debris disk with a silicate feature, a brown dwarf companion with a photospheric spectrum, and potential signs of additional unseen planets affecting disk structure.

Contribution

First mid-IR spectrum of $ au$ Tel B and detailed analysis of the debris disk and companion orbit, suggesting possible unseen planets influencing disk morphology.

Findings

Detection of a 20 μm silicate feature in the debris disk.

First 11-21 μm spectrum of $ au$ Tel B showing a bare photosphere.

Companion's orbit consistent with apocentre, but disk appears axisymmetric and possibly misaligned.

Abstract

We report JWST MIRI MRS observations of the $\beta$ Pictoris moving group member, $\eta$ Telescopii ($\eta$ Tel) A and its brown dwarf binary companion, $\eta$ Tel B. Following PSF subtraction, we recover the spatially resolved flux from the debris disk around $\eta$ Tel A, along with the position of the companion exterior to the disk. We present a new 5-26 $\mu$m epoch of spectroscopy for the disk, in which we discover a 20 $\mu$m silicate feature. We also present the first ever 11-21 $\mu$m spectrum of $\eta$ Tel B, which indicates a bare photosphere. We derive a new epoch of relative astrometry for the companion, extending the baseline of measurements to 25 years, and find that its current location is consistent with the apocentre of an eccentric, long-period orbit. The companion's orbit is close enough to the disk that it should significantly perturb the planetesimals within it, resulting in a detectable mid-IR pericentre glow and near-alignment with the companion. Contrary to expectations, however, we find that the disk appears to be axisymmetric and potentially misaligned with the companion in the MIRI MRS data. We posit that this may be due to the presence of an additional, yet-undetected 0.7-30 $M_J$ planet orbiting interior to the disk with a semi-major axis of 3-19 au.