Probing the cold dust emission in the AB Aur disk: a dust trap in a decaying vortex?

TL;DR

This study uses high-resolution observations and simulations to investigate dust trapping in the AB Aur disk, revealing evidence of a decaying vortex affecting dust distribution and providing insights into planet formation potential.

Contribution

It presents the first observational evidence of a decaying gas vortex in a protoplanetary disk and links it to dust size segregation and planet formation conditions.

Findings

Azimuthal flux ratio variations indicate dust size segregation.

Intensity variations suggest vortex decay due to turbulence.

Estimated solid mass in the ring is about 30 Earth masses.

Abstract

One serious challenge for planet formation is the rapid inward drift of pebble-sized dust particles in protoplanetary disks. Dust trapping at local maxima in the disk gas pressure has received much theoretical attention but still lacks observational support. The cold dust emission in the AB Aur disk forms an asymmetric ring at a radius of about 120 au, which is suggestive of dust trapping in a gas vortex. We present high spatial resolution (0".58x0".78 ~ 80x110 au) NOEMA observations of the 1.12 mm and 2.22 mm dust continuum emission from the AB Aur disk. Significant azimuthal variations of the flux ratio at both wavelengths indicate a size segregation of the large dust particles along the ring. Our continuum images also show that the intensity variations along the ring are smaller at 2.22 mm than at 1.12 mm, contrary to what dust trapping models with a gas vortex have predicted. Our two-fluid (gas+dust) hydrodynamical simulations demonstrate that this feature is well explained if the gas vortex has started to decay due to turbulent diffusion, and dust particles are thus losing the azimuthal trapping on different timescales depending on their size. The comparison between our observations and simulations allows us to constrain the size distribution and the total mass of solid particles in the ring, which we find to be of the order of 30 Earth masses, enough to form future rocky planets.