A concentration of centimeter-sized grains in the Oph IRS 48 dust trap

TL;DR

This study uses high-resolution ALMA and VLA observations to investigate dust grain distribution in the Oph IRS 48 disk, providing evidence that larger particles are more azimuthally concentrated, supporting dust trapping theories in planet formation.

Contribution

First direct evidence that centimeter-sized grains are more azimuthally concentrated than smaller dust in a protoplanetary disk, supporting dust trapping models.

Findings

Larger particles are more azimuthally concentrated than smaller ones.

The azimuthal extent of centimeter emission is narrower than millimeter emission.

Evidence of ionized gas emission from the star.

Abstract

Azimuthally asymmetric dust distributions observed with ALMA in transition disks have been interpreted as dust traps. We present VLA Ka band (34 GHz or 0.9 cm) and ALMA Cycle 2 Band 9 (680 GHz or 0.45 mm) observations at 0.2" resolution of the Oph IRS 48 disk, which suggest that larger particles could be more azimuthally concentrated than smaller dust grains, assuming an axisymmetric temperature field or optically thin 680 GHz emission. Fitting an intensity model to both data demonstrates that the azimuthal extent of the millimeter emission is 2.3 $\pm0.9$ times as wide as the centimeter emission, marginally consistent with the particle trapping mechanism under the above assumptions. The 34 GHz continuum image also reveals evidence for ionized gas emission from the star. Both the morphology and the spectral index variations are consistent with an increase of large particles in the center of the trap, but uncertainties remain due to the continuum optical depth at 680 GHz. Particle trapping has been proposed in planet formation models to allow dust particles to grow beyond millimeter sizes in the outer regions of protoplanetary disks. The new observations in the Oph IRS 48 disk provide support for the dust trapping mechanism for centimeter-sized grains, although additional data is required for definitive confirmation.