The Oxygen Budget in Low-Mass Protostellar Outflows: the NGC1333-IRAS4A R1 Shock Observed in [OI] at 63 Microns with SOFIA-GREAT
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Lars Kristensen
Neils Bohr Institute
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Oxygen (O) is the third-most abundant element in the Universe after hydrogen and helium. Despite its high elemental abundance, a good picture of where oxygen is located in low-mass protostellar outflows and jets is missing: we cannot account for > 60% of the oxygen budget in these objects. This hole in our picture means that we currently do not have a good understanding of the dominant cooling processes in outflows jets, despite the fact that [OI] emission at 63 micron is one of the dominant cooling lines, nor how cooling processes evolve with protostellar evolution. To test if the oxygen is in atomic form, SOFIA-GREAT observed the R1 position of the bright molecular outflow from NGC1333-IRAS4A. The [OI] 63 micron line is detected and spectrally resolved, and the profile is similar to that of high-velocity (HV) H2O and CO 16-15, the latter observed simultaneously with [OI]. A radiative transfer analysis suggests that ~15% of the oxygen is in atomic form toward this shock position. These early results clearly demonstrate that a large fraction of the observed [OI] emission is part of the molecular outflow, and that GREAT is capable of delivering stunning scientific results. Further observations are now required to verify if the results obtained here are part of a general trend, or if this particular shock is unique.

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