  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 [OI] and [CII] as part of the Open-time
large program GASPS. We complement this with continuum data and ground-based
12CO 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 63
micron. The other lines that were observed, [OI] at 145 micron and [CII] at 157
micron, 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 times 10^-4 Msun (total solid
mass of 3 times 10^-3 Msun) and a gas mass of (0.5--5) times 10^-3 Msun. The
gas-to-dust mass may be lower than the standard interstellar value of 100.
