WATCH - WATer Chemistry with Herschel

Water is one of the most abundant species in starforming regions and plays important roles in both the energy balance, acting as a coolant, and the chemistry of star formation. Many of the species involved in the water chemistry emit in the farinfrared and are thus not observable from ground based facilities because of atmospheric absorption. Therefore, the Herschel Space Observatory provides a unique opportunity to study the chemical reactions involved in the formation and destruction of water and to probe the energetic processes in starforming regions. Previous results from Herschel have shown that two species, OH+ and H2O+, that were thought to be important in the water chemistry of young stellar objects, are now mainly attributed to foreground clouds. These results raised the question on which chemical paths the formation and destruction of water takes place in the interior of protostellar envelopes.In this proposal, we plan to observe the different formation and destruction routes of water in a sample of eight nearby young stellar objects, which were chosen to cover a broad range of masses, luminosities and evolutionary stages. We propose to observe H3O+ and HCO+, two species that are closely linked to the formation and destruction of H2O and require high temperatures for excitation, in serveral highJ lines. This effort is complementary to the observations of H2O and OH done in the .Water in starforming regions with Herschel (WISH). key project. The combination of the information from the H2O, OH, H3O+ and HCO+ emission will tell us on which routes the formation and destruction of H2O in protostellar envelopes proceeds. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]