The total gas mass of a protoplanetary disk is a fundamental , but poorly determined , quantity .
A new technique ( 12 ) has been demonstrated to assess directly the bulk molecular gas reservoir of molecular hydrogen using the HD J=1-0 line at 112 \mu m. In this work we present a Herschel Space Observatory Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA . survey of six additional T Tauri disks in the HD line .
Line emission is detected at > 3 \sigma significance in two cases : DM Tau and GM Aur .
For the other four disks , we establish upper limits to the line flux .
Using detailed disk structure and ray tracing models , we calculate the temperature structure and dust mass from modeling the observed spectral energy distributions , and include the effect of UV gas heating to determine the amount of gas required to fit the HD line .
The range of gas masses are 1.0-4.7 \times 10 ^ { -2 } for DM Tau and 2.5-20.4 \times 10 ^ { -2 } for GM Aur .
These values are larger than those found using CO for GM Aur , while the CO-derived gas mass for DM Tau is consistent with the lower end of our mass range .
This suggests a CO chemical depletion from the gas phase of up to a factor of five for DM Tau and up to two orders of magnitude for GM Aur .
We discuss how future analysis can narrow the mass ranges further .