Tracing Remnant Gas in Planet Forming Debris Disk Systems

Recent studies of gas emission lines with Spitzer and submillimeter telescopes have shown that 10100 Myr old stars with debris disks have too little gas left to form Jupiter like gas giant planets. Whether enough gas remains in these systems to form ice giant planets is still unanswered. The OI emission line at 63 micron is one of the most sensitive tracers of gas mass in the icegiant region of 1050 AU in disks, and Herschel PACS is therefore uniquely suited to trace the remnant gas in planetforming disks. We propose to obtain PACS line spectroscopy of OI (63 micron) for two nearby young stars, HR 8799 and HD 15115, which are two systems with detected giant planets or signs of planet formation, while still harbouring prominent debris disks that could be in the process of forming ice giants such as Neptune and Uranus. The proposed observations will probe down to gas masses of 0.01 Earth masses, and allow us to constrain prospects for ice giant formation, measure gastodust ratios in evolved disks to compare with planet formation / disk evolution models, and put constraints on whether the dust dynamics in these systems is driven by the remnant gas or by the radiation.Note: this proposal is submitted under the Swiss part of the HIFI Guaranteed Time program; HIFI PI: Frank Helmich, HIFI Swiss Lead CoI: Arnold Benz. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]