Gas in the protoplanetary disc of HD?169142: Herschel's view

摘要

In an effort to simultaneously study the gas and dust components of thedisc surrounding the young HerbigAe star HD169142,we present far-IR observations obtained with the PACS instrumentonboard the Herschel Space Observatory. This workis part of the open time key program GASPS, which is aimed at studyingthe evolution of protoplanetary discs. Toconstrain the gasproperties in the outer disc, we observed the star at several keygas-lines, including [OI]63.2 and 145.5m,[CII]157.7m,CO72.8 and 90.2m, and o-H2O78.7and 179.5m.We only detect the [OI]63.2m line in our spectra, and derive upper limitsfor the other lines. We complement our data set withPACSphotometry and 12/13COdataobtained with the Submillimeter Array. Furthermore, we derive accuratestellar parameters from optical spectra and UV tommphotometry. We model the dust continuum with the3Dradiative transfer code MCFOST and use this model as aninput to analyse the gas lines with the thermo-chemical code P RODIM O. Ourdataset is consistent with a simple model in which the gas and dust arewell-mixed in a disc with a continuous structure between20and 200AU, but this is not a unique solution. Our modellingeffort allows us to constrain the gas-to-dust mass ratio as well as therelative abundance of the PAHs in the disc by simultaneously fittingthe lines of several species that originate in different regions. Ourresults are inconsistent with a gas-poor disc with a largeUVexcess; agas mass of 5.02.010-3is still present in this disc, in agreement with earlierCOobservations. Key words: planetary systems -circumstellar matter - stars: pre-main sequence - protoplanetary disks- infrared: planetary systems