Modest dust settling in the IRAS04302+2247 Class I protoplanetary disk

TL;DR

This study uses multi-wavelength radio observations and radiative transfer modeling to investigate dust grain sizes and vertical settling in the Class I protoplanetary disk IRAS04302+2247, revealing an intermediate stage of dust settling.

Contribution

It provides the first lower limit on grain scale height in a Class I disk and demonstrates modest dust settling at this evolutionary stage.

Findings

Dust grains are smaller than 1cm in outer disk regions.

Millimeter dust scale height is between 1 and 6 au at 100 au radius.

Dust settling is intermediate between Class 0 and Class II sources.

Abstract

We present new VLA observations, between 6.8mm and 66mm, of the edge-on Class~I disk IRAS04302+2247. Observations at 6.8mm and 9.2mm lead to the detection of thermal emission from the disk, while shallow observations at the other wavelengths are used to correct for emission from other processes. The disk radial brightness profile transitions from broadly extended in previous ALMA 0.9mm and 2.1mm observations to much more centrally brightened at 6.8mm and 9.2mm, which can be explained by optical depth effects. The radiative transfer modeling of the 0.9mm, 2.1mm, and 9.2mm data suggests that the grains are smaller than 1cm in the outer regions of the disk and allows us to obtain the first lower limit for the scale height of grains emitting at millimeter wavelengths in a protoplanetary disk. We find that the millimeter dust scale height is between 1au and 6au at a radius 100au from the central star, while the gas scale height is estimated to be about 7au, indicating a modest level of settling. The estimated dust height is intermediate between less evolved Class 0 sources, that are found to be vertically thick, and more evolved Class II sources, which show a significant level of settling. This suggests that we are witnessing an intermediate stage of dust settling.