Detection of Substructures in Young Transition Disk WL 17

TL;DR

This study investigates the dust properties and substructures of the young transition disk WL 17 using high-sensitivity ALMA data, revealing potential disk flaring and substructures that inform planet formation processes.

Contribution

The paper combines multi-frequency ALMA data with simple geometric models to estimate optical depth and detect disk substructures, providing new insights into dust distribution and disk morphology.

Findings

Optical depth at 233 GHz peaks at ~0.3, suggesting limited self-scattering.

First detection of substructure in WL 17's disk at 233 GHz.

Evidence of disk flaring with brighter lobes along the major axis.

Abstract

WL 17 is a young transition disk in the Ophiuchus L1688 molecular cloud complex. Even though WL 17 is among the brightest disks in L1688 and massive enough to expect dust self-scattering, it was undetected in polarization down to ALMA's instrument sensitivity limit. Such low polarization fractions could indicate unresolved polarization within the beam or optically thin dust emission. We test the latter case by combining the high sensitivity 233 GHz Stokes I data from the polarization observations with previous ALMA data at 345 GHz and 100 GHz. We use simple geometric shapes to fit the observed disk visibilities in each band. Using our simple models and assumed dust temperature profiles, we estimate the optical depth in all three bands. The optical depth at 233 GHz peaks at $\tau_{233} \sim 0.3$, which suggests the dust emission may not be optically thick enough for dust self-scattering to be efficient. We also find the higher sensitivity 233 GHz data show substructure in the disk for the first time. The substructure appears as brighter lobes along the major axis, on either side of the star. We attempt to fit the lobes with a simple geometric model, but they are unresolved in the 233 GHz data. We propose that the disk may be flared at 1 mm such that there is a higher column of dust along the major axis than the minor axis when viewed at an inclination. These observations highlight the strength of high sensitivity continuum data from dust polarization observations to study disk structures.