Water and methanol in low-mass protostellar outflows: gas-phase
  synthesis, ice sputtering and destruction
  Water in outflows from protostars originates either as a result of gas-phase
synthesis from atomic oxygen at T > 200 K, or from sputtered ice mantles
containing water ice. We aim to quantify the contribution of the two mechanisms
that lead to water in outflows, by comparing observations of gas-phase water to
methanol (a grain surface product) towards three low-mass protostars in
NGC1333. In doing so, we also quantify the amount of methanol destroyed in
outflows. To do this, we make use of JCMT and Herschel-HIFI data of H2O, CH3OH
and CO emission lines and compare them to RADEX non-LTE excitation simulations.
We find up to one order of magnitude decrease in the column density ratio of
CH3OH over H2O as the velocity increases in the line wings up to ~15 km/s. An
independent decrease in X(CH3OH) with respect to CO of up to one order of
magnitude is also found in these objects. We conclude that gas-phase formation
of H2O must be active at high velocities (above 10 km/s, relative to the source
velocity) to re-form the water destroyed during sputtering. In addition, the
transition from sputtered water at low velocities to formed water at high
velocities must be gradual. We place an upper limit of two orders of magnitude
on the destruction of methanol by sputtering effects.
