The Flying Saucer edge-on disc's Near Infrared silhouette revealed by the JWST JEDIce program

TL;DR

This study uses JWST observations to analyze the dust distribution and grain sizes in the edge-on Flying Saucer protoplanetary disc, revealing insights into dust settling and grain size distribution at different wavelengths.

Contribution

First near-infrared silhouette observations of the Flying Saucer disc constrain dust and grain size distributions, providing new insights into dust settling in protoplanetary discs.

Findings

Midplane radial extent of small dust grains is ~235 au.

Large-grain disc extent from millimetre data is 190 au.

Dust settling is inefficient for grains as large as tens of microns.

Abstract

Edge-on discs offer a unique opportunity to probe radial and vertical dust and gas distributions in the protoplanetary phase. This study aims to investigate the distribution of micron-sized dust particles in the Flying Saucer (BKLT J162813-243139) in Rho Ophiuchi, leveraging the unique observational conditions of a bright infrared background that enables the edge-on disc to be seen in both silhouette and scattered light at certain, specific wavelengths. As part of the JWST Edge-on Disc Ice program ('JEDIce'), we use NIRSpec IFU observations of the Flying Saucer, serendipitously observed against a PAH-emitting background, to constrain the dust distribution and grain sizes through radiative transfer modelling. Observation of the Flying Saucer in silhouette at 3.29 microns reveals that the midplane radial extent of small dust grains is ~235 au, larger than the large-grain disc extent previously determined to be 190 au from millimetre data. The scattered light observed in emission probes micron sized icy grains at large vertical distances above the midplane. The vertical extent of the disc silhouette is similar at visible, near-IR, and mid-IR wavelengths, corroborating the conclusion that dust settling is inefficient for grains as large as tens of microns, vertically and radially.