Remnant gas in evolved circumstellar disks: Herschel PACS observations of 10-100 Myr old disk systems

TL;DR

This study uses Herschel PACS spectroscopy to detect and model remnant gas in evolved circumstellar disks around three systems, revealing varied gas masses and disk structures relevant to planet formation.

Contribution

It provides new gas mass constraints and disk models for three evolved systems, highlighting the diversity of disk evolution stages.

Findings

RX J1852.3-3700 shows [OI] detection, indicating gas presence.

Upper limits on gas mass for HR 8799 and HD 377 are 0.1-20 Mearth.

Two disk scenarios explain the [OI] detection in RX J1852.3-3700.

Abstract

We present Herschel PACS spectroscopy of the [OI] 63 micron 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 x 10^-18 W m^-2 and 9.9 x 10^-18 W m^-2 respectively. We find an [OI] detection for RX J1852.3-3700 at 12.3 +- 1.8 x 10^-18 W m^-2. We use thermo-chemical disk models to model the gas emission, using constraints on the [OI] 63 micron, 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 Mearth. For RX J1852.3-3700, we find two distinct disk scenarios that could explain the detection of [OI] 63 micron 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 ~16 Mearth of gas, or (ii) an optically thick gas disk, truncated at ~70 AU, with a gas mass of 150 Mearth. We discuss the implications of these results for the formation and evolution of planets in these three systems.