2013ApJ...776...21H

The Herschel Space Observatory was used to observe ∼120 pre-main-sequence stars in Taurus as part of the GASPS Open Time Key project. Photodetector Array Camera and Spectrometer was used to measure the continuum as well as several gas tracers such as [O I] 63 µm, [O I] 145 µm, [C II] 158 µm, OH, H₂O, and CO. The strongest line seen is [O I] at 63 µm. We find a clear correlation between the strength of the [O I] 63 µm line and the 63 µm continuum for disk sources. In outflow sources, the line emission can be up to 20 times stronger than in disk sources, suggesting that the line emission is dominated by the outflow. The tight correlation seen for disk sources suggests that the emission arises from the inner disk (<50 AU) and lower surface layers of the disk where the gas and dust are coupled. The [O I] 63 µm is fainter in transitional stars than in normal Class II disks. Simple spectral energy distribution models indicate that the dust responsible for the continuum emission is colder in these disks, leading to weaker line emission. [C II] 158 µm emission is only detected in strong outflow sources. The observed line ratios of [O I] 63 µm to [O I] 145 µm are in the regime where we are insensitive to the gas-to-dust ratio, neither can we discriminate between shock or photodissociation region emission. We detect no Class III object in [O I] 63 µm and only three in continuum, at least one of which is a candidate debris disk.