Water in Star-forming regions with Herschel (WISH)

Ewine van Dishoeck (Sterrewacht Leiden)

Rafael Bachiller, Asunción Fuente, Joaquín Santiago-García, Mario Tafalla.

Water is a key molecule for determining the physical and chemical structure of star-forming regions because of its large abundance variations -both in the gas and in the ice- between warm and cold regions. In this HIFI-led Key Program, we propose a comprehensive set of water observations toward a large sample of well-characterized protostars, covering a wide range of masses and luminosities -from the lowest to the highest mass protostars- and a large range of evolutionary stages -from the first stages represented by the pre-stellar cores to the last stages represented by the pre-main sequence stars surrounded only by their protostellar disks. Lines of H₂O, H₂¹⁸O, H₂¹⁷O and chemically related hydrides will be observed. In addition, selected high-frequency lines of CO isotopes, [OI] as well as dust continuum maps will be obtained with HIFI and PACS, and will be complemented by ground-based HDO, CO and continuum maps to ensure a self-consistent data set for analysis. Limited mapping information on arcmin scale provides information on local variations due to outflows and clustered star formation. Together, the data will elucidate the physical processes responsible for the warm gas, probe dynamical processes associated with forming stars and planets, reveal the chemical evolution of water and the oxygen-reservoir, and test basic gas-grain chemical interactions. They will form an unique legacy for the community as a complement to future ground-based programs and for planning future space missions.