Antranik Sefilian | Searcharxiv

arXiv2024

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

We report JWST MIRI MRS observations of the $β$ Pictoris moving group member, $η$ Telescopii ($η$ Tel) A and its brown dwarf binary companion, $η$ Tel B. Following PSF subtraction, we recover the spatially resolved flux from the debris disk around $η$ Tel A, along with the position of the companion exterior to the disk. We present a new 5-26 $μ$m epoch of spectroscopy for the disk, in which we discover a 20 $μ$m silicate feature. We also present the first ever 11-21 $μ$m spectrum of $η$ 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.

astro-ph.EP↗

arXiv2023

The case of HD 106906 debris disc: A binary's revenge

Debris disc architecture presents [exo-]planetary scientists with precious clues for processes of planet formation and evolution, including constraints on planetary mass perturbers. This is particularly true of the disc in HD 106906, which in early HST, then follow up polarimetric observations, presented asymmetries and needle-like features that have been attributed to perturbations by a massive, and unusually distant external planetary companion. Here, we revisit the long-term secular dynamical evolution of the HD 106906 disc allowing for the combined gravitational action of the planetary companion and the inner stellar binary which holds the system together. We argue that the binary is strong enough to impose a dynamical break at the disc's location, resulting in distinctive observational signatures which we render via simulated surface density maps and vertical structure profiles. Within uncertainties on the planet's orbit, we show that the disc can go from being fully dominated by the inner binary to significantly so, and is hardly ever outside its reach. The extent of binary dominance impacts the disc's mean eccentricity, a metric which we map as a function of the planet's semi-major axis and orbital eccentricity, with and without radiation pressure. We can thus constrain the planet's orbit to ease the tension between evident axisymmetry in the millimeter, and apparent asymmetry in scattered light. We discuss phase space structure, then inclination distribution, arguing for the relevance of our results to a variety of hierarchical systems, as we set the stage for generalizations that allow for disc self-gravity and collisional evolution.

astro-ph.EP↗