| Description |
Most low mass stars form near OB associations and are hence subject to the harsh feedback of massive stars. Proplyds are in this situation. They are young stars, surrounded by a protoplanetary disk which is being photo-evaporated by the far-UV (FUV) photons emitted by massive stars. This photo-evaporation process determines the mass-loss and hence lifetime of these disks, which may result in severe constraints on the planet formation timescale. The photo-evaporation flow results from the formation of a photodissocaition region (PDR) at the surface of the disk, where FUV photons heat the atomic and molecular gas. The bright far-infrared cooling lines of atomic and molecular gas, observable with Herschel, are therefore the ideal tracers to understand the mechanisms at play in the PDRs at the surface of the disks. Unfortunately, proplyds have not been observed with Herschel. With this proposal, we will obtain key cooling lines -- OI, CII and high J CO-- emitted by the dense and highly irradiated PDRs of three carefully selected proplyds in the Orion and Carina Nebulae. We will then analyze these observations in the frame of PDR and disk models, in order to provide a clearer picture of the photoevaporation process. For these observations we require 10.3 hours. |
