# New Constraints From Dust Lines On The Surface Densities Of Protoplanetary Disks

## TL;DR

This study introduces a new method to determine protoplanetary disk surface densities using dust lines, revealing larger disk masses than previous estimates and implications for disk stability and planet formation.

## Contribution

Developed a robust, opacity-independent method to measure disk surface density from dust lines, providing more accurate mass estimates and insights into disk stability.

## Key findings

- Disk masses are 9-27% of stellar mass, larger than previous estimates.
- Most disks are stable against gravitational collapse, except one.
- Dust-based mass estimates are 2-15 times higher than optically thin dust emission estimates.

## Abstract

We present new determinations of disk surface density, independent of an assumed dust opacity, for a sample of 7 bright, diverse protoplanetary disks using measurements of disk dust lines. We develop a robust method for determining the location of dust lines by modeling disk interferometric visibilities at multiple wavelengths. The disks in our sample have newly derived masses that are 9-27% of their host stellar mass, substantially larger than the minimum mass solar nebula. All are stable to gravitational collapse except for one which approaches the limit of Toomre-Q stability. Our mass estimates are 2-15 times larger than estimates from integrated optically thin dust emission. We derive depleted dust-to-gas ratios with typical values of ~$10^{-3}$ in the outer disk. Using coagulation models we derive dust surface density profiles that are consistent with millimeter dust observations. In these models, the disks formed with an initial dust mass that is a factor of ~10 greater than is presently observed. Of the three disks in our sample with resolved CO line emission, the masses of HD 163296, AS 209, and TW Hya are roughly 3, 115, and 40 times more massive than estimates from CO respectively. This range indicates that CO depletion is not uniform across different disks and that dust is a more robust tracer of total disk mass. Our method of determining surface density using dust lines is robust even if particles form as aggregates and is useful even in the presence of dust substructure caused by pressure traps. The low Toomre-Q values observed in this sample indicate that at least some disks do not accrete efficiently.