| Description |
The heterodyne instrument HIFI aboard Herschel is the only instrument that will be able to observe molecular oxygen from astronomical objects outside the solar system for decades to come. We encourage the HOTAC to endorse this proposal that aims to understand the formation and destruction of O2 in the star forming interstellar medium (ISM), including its important interplay with the energy balance and chemistry of the gas and dust. We select one of the very few regions where O2 has been detected with Herschel, i.e. the nearby (120 pc) rho Oph A cloud core. Its proximity allows high spatial resolution, where different physical regions are distinctly resolved, viz. dense prestellar cores, shocks due an outflow from a Class 0 protostar and an extended photon-dominated region (PDR). Of importance is to understand to what extent O2 sources are compact and dense or more uniformly extended. Mapping these regions in the 487 GHz O2 line with HIFI, and complementing with a higher excitation line toward the shock region, will yield convincing evidence which of these are the main contributors to the O2 emission and identify the major physical and chemical processes responsible for its abundance. This has been inferred to be lower by orders of magnitude than what had been predicted by early models. Oxygen chemistry forms the backbone of astrochemistry, and oxygen-bearing species generally dominate the cooling of molecular gas. This proposal seeks to understand the basic processes that dominate the major species involved in oxygen chemistry. With our proposed observing programme, in combination with adequate theoretical modelling, a long standing riddle will finally find its resolution - a true legacy of Herschel and HIFI! |
