Remnant Gas in Evolved Circumstellar Disks: Herschel PACS Observations of 10-100 Myr Old Disk Systems

Abstract

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 6.8 × 10^-18 W m^-2 and 9.9 × 10^-18 W m^-2, respectively. We find an [O I] detection for RX J1852.3-3700 at (12.3 ± 1.8) × 10^-18 W m^-2. 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.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.