Parametric model for circumstellar disks gas mass

Disk mass measurements have therefore relied on large and uncertain extrapolations from the dust to the gas. We have developed a grid of models to study the dependencies of isotopologue CO line strengths on disk structure and temperature parameters and find that a combination of ^13^CO and C^18^O observations provides a robust measure of the gas mass.

We apply this technique to Submillimeter Array observations of nine circumstellar disks and published measurements of six well studied disks. We find evidence for selective photodissociation of C^18^O and determine masses to within a factor of about three. The inferred masses for the nine disks in our survey range from 0.7 to 6 M_Jup_, and all are well below the extrapolation from the interstellar medium gas-to-dust ratio of 100.