A novel way of measuring the gas disk mass of protoplanetary disks using N₂H⁺ and C18O

Measuring the gas mass of protoplanetary disks, the reservoir available for giant planet formation, has proven to be difficult. We currently lack a far-infrared observatory capable of observing HD, and the most common gas mass tracer, CO, suffers from a poorly constrained CO-to-H₂ ratio. I will present recently published work where we investigated if N₂H⁺, a chemical tracer of CO poor gas, can be used to observationally measure the CO-to-H2 ratio in disks and correct their CO-based gas masses. To test this, we set up thermochemical models for the three disks (TW Hya, DM Tau and GM Aur) where HD 1-0 has been previously detected and used to independently measure the disk gas mass. We show that the CO-to-H₂ ratio and gas mass can be measured from N₂H⁺ and C¹⁸O line fluxes and that these gas masses agree with values obtained from HD within their respective uncertainties. . These results demonstrate the potential of using the combination of N₂H⁺ and C¹⁸O to measure gas masses of protoplanetary disks.