| Description |
We propose a survey of water lines toward an unbiased flux limitedsample of low-mass protostars newly discovered in recent Spitzer andHerschel Gould Belt imaging surveys. Water has long been speculated tobe a key molecule in the chemistry and physics of star-formingregions, but its actual role is only now starting to emerge thanks toHerschel. Initial HIFI data reveal surprisingly complex water emissionprofiles, which uniquely trace the different dynamical processesduring the embedded phase of star formation (outflows, jets, shocks,infall, expansion). By using lines originating from different energylevels, the water abundance in the cold and warm gas can be determinedas function of velocity and thus the chemical processes that shapethem (gas-grain interactions, high temperature reactions). Theortho/para and HDO/H2O ratios hold important clues on the temperaturehistory of the clouds and on the journey of water from cores to disksand planets. Combination with PACS data on water and related species(O, OH, CO) can determine the total gas cooling budget and canquantify the .feedback. of the protostar on its surroundings in termsof UV radiation and shocks. The unbiased WILL sample allows all of these questions to be studiedas function of source characteristics and protostellar evolution in astatistically significant way, thus charting the processes that shapethe emerging young star and disk in the critical period from thecollapse phase to the envelope dispersion stage. No other space-basedheterodyne mission will be available to provide velocity resolvedwater lines for at least 30 years, making this program a true HerschelGould Belt line emission legacy. |
