Presentation #319.03 in the session Exoplanet Formation of Planets and Protoplanetary Disks I.
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.