Oxygen budget in low-mass protostars: the NGC1333-IRAS4A R1 shock
  observed in [OI] at 63 um with SOFIA-GREAT
  In molecular outflows from forming low-mass protostars, most oxygen is
expected to be locked up in water. However, Herschel observations have shown
that typically an order of magnitude or more of the oxygen is still unaccounted
for. To test if the oxygen is instead in atomic form, SOFIA-GREAT observed the
R1 position of the bright molecular outflow from NGC1333-IRAS4A. The [OI] 63 um
line is detected and spectrally resolved. From an intensity peak at +15 km/s,
the intensity decreases until +50 km/s. 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. The CO abundance is inferred to be
~10^-4 by a similar analysis, suggesting that this is the dominant oxygen
carrier in the HV component. These results demonstrate that a large portion of
the observed [OI] emission is part of the outflow. Further observations are
required to verify whether this is a general trend.
