2012ApJ...755....8G

We present Herschel PACS spectroscopy of the [O I] 63 µm gas line for three circumstellar disk systems showing signs of significant disk evolution and/or planet formation: HR 8799, HD 377, and RX J1852.3-3700. [O I] is undetected toward HR 8799 and HD 377 with 3σ upper limits of 6.8x10^–18 W/m2 and 9.9x10^–18 W/m2, respectively. We find an [O I] detection for RX J1852.3-3700 at (12.3±1.8)x10^–18 W/m2. We use thermo-chemical disk models to model the gas emission, using constraints on the [O I] 63 µm and ancillary data to derive gas mass upper limits and constrain gas-to-dust ratios. For HD 377 and HR 8799, we find 3σ upper limits on the gas mass of 0.1-20 M_⊕. For RX J1852.3-3700, we find two distinct disk scenarios that could explain the detection of [O I] 63 µm and CO(2-1) upper limits reported in the literature: (1) a large disk with gas co-located with the dust (16-500 AU), resulting in a large tenuous disk with ∼16 M_⊕ of gas, or (2) an optically thick gas disk, truncated at ∼70 AU, with a gas mass of 150 M_⊕. We discuss the implications of these results for the formation and evolution of planets in these three systems.