<i>Herschel</i>-PACS observation of the 10 Myr old T Tauri disk TW Hya

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 <i>Herschel<i/>–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 <sup>12<sup/> CO 3–2 and <sup>13<sup/>CO 3–2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code <i>MCFOST<i/> and the thermo-chemical code <i>ProDiMo<i/> to derive the gas and dust masses. We detect the [O i] line at 63 <i>μ<i/>m. The other lines that were observed, [O i] at 145 <i>μ<i/>m and [C ii] at 157 <i>μ<i/>m, are not detected. No extended emission has been found. Preliminary modeling of the photometric and line data assuming [ <sup>12<sup/>CO] /[ <sup>13<sup/>CO] = 69 suggests a dust mass for grains with radius <1 mm of ~1.9 × 10<sup>-4<sup/> (total solid mass of 3 × 10<sup>-3<sup/> ) and a gas mass of (0.5–5) × 10<sup>-3<sup/> . The gas-to-dust mass may be lower than the standard interstellar value of 100.