| 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! |
