We present Herschel PACS spectroscopy of the [ OI ] 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 .
[ OI ] is undetected toward HR 8799 and HD 377 with 3 \sigma upper limits of 6.8 \times 10 ^ { -18 } W m ^ { -2 } and 9.9 \times 10 ^ { -18 } W m ^ { -2 } respectively .
We find an [ OI ] detection for RX J1852.3-3700 at 12.3 \pm 1.8 \times 10 ^ { -18 } W m ^ { -2 } .
We use thermo-chemical disk models to model the gas emission , using constraints on the [ OI ] 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 3 \sigma upper limits on the gas mass of 0.1–20 M _ { \mathrm { \oplus } } .
For RX J1852.3-3700 , we find two distinct disk scenarios that could explain the detection of [ OI ] 63 µm and CO ( 2–1 ) upper limits reported from the literature : ( i ) a large disk with gas co-located with the dust ( 16–500 AU ) , resulting in a large tenuous disk with \sim 16 M _ { \mathrm { \oplus } } of gas , or ( ii ) an optically thick gas disk , truncated at \sim 70 AU , with a gas mass of 150 M _ { \mathrm { \oplus } } .
We discuss the implications of these results for the formation and evolution of planets in these three systems .