2010A&A...518L.125T

Planets are formed in disks around young stars. With an age of ∼10Myr, 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 [OI] and [CII] 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 [OI] line at 63µm. The other lines that were observed, [OI] at 145µm and [CII] at 157µm, 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 <1mm of ∼1.9x10^–4M_☉ (total solid mass of 3x10^–3M_☉) and a gas mass of (0.5-5)x10^–3M_☉. The gas-to-dust mass may be lower than the standard interstellar value of 100.