Planets are formed in disks around young stars. With an age of ∼10 Myr, TW Hya is one of the nearest T Tauri stars that is still surrounded by a relatively massive disk. In addition a large number of molecules has been found in the TW Hya disk, making TW Hya the perfect test case in a large survey of disks with Herschel-PACS to directly study their gaseous component. We aim to constrain the gas and dust mass of the circumstellar disk around TW Hya. We observed the fine-structure lines of [O i] and [C ii] as part of the open-time large program GASPS. We complement this with continuum data and ground-based 12 CO 3-2 and 13CO 3-2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code MCFOST and the thermo-chemical code ProDiMo to derive the gas and dust masses. We detect the [O i] line at 63 μm. The other lines that were observed, [O i] at 145 μm and [C ii] at 157 μm, are not detected. No extended emission has been found. Preliminary modeling of the photometric and line data assuming [ 12CO] /[13CO] = 69 suggests a dust mass for grains with radius <1 mm of ∼1.9 × 10-4 M⊙ (total solid mass of 3 × 10-3 M⊙) and a gas mass of (0.5-5) × 10 -3 M⊙. The gas-to-dust mass may be lower than the standard interstellar value of 100.
- circumstellar disks