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 i
n 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.
(abridged) We correlated near-infrared stellar H-Ks colour excesses of background stars from NTT/SOFI with the far-IR optical depth map, tauFIR, derived from Herschel 160, 250, 350, and 500 um data. The Herschel maps were also used to construct a mod
el for the cloud to examine the effect of temperature gradients on the estimated optical depths and dust absorption cross-sections. A linear correlation is seen between the colour H-Ks and tauFIR up to high extinctions (AV ~ 25). The correlation translates to the average extinction ratio A250um/AJ = 0.0014 +/- 0.0002, assuming a standard near-infrared extinction law and a dust emissivity index beta=2. Using an empirical NH/AJ ratio we obtain an average absorption cross-section per H nucleus of sigmaH(250um) = (1.8 +/- 0.3) * 10^(-25) cm^2 / H-atom, corresponding to a cross-section per unit mass of gas kappaG(250 um) = 0.08 +/- 0.01 cm^2 / g. The cloud model however suggests that owing to the bias caused by temperature changes along the line-of-sight these values underestimate the true cross-sections by up to 40% near the centre of the core. Assuming that the model describes the effect of the temperature variation on tauFIR correctly, we find that the relationship between H-Ks and tauFIR agrees with the recently determined relationship between sigmaH and NH in Orion A. The derived far-IR cross-section agrees with previous determinations in molecular clouds with moderate column densities, and is not particularly large compared with some other cold cores. We suggest that this is connected to the core not beng very dense (the central density is likely to be ~10^5 cm^-3) and judging from previous molecular line data, it appears to be at an early stage of chemical evolution.
