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 H 2 O, CH 3 OH 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 CH 3 OH over H 2 O as the velocity increases in the line wings up to ∼15 km s −1 . An independent decrease in X(CH 3 OH) with respect to CO of up to one order of magnitude is also found in these objects. We conclude that gas-phase formation of H 2 O must be active at high velocities (above 10 km s −1 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.

Aims. The aim of this study is to examine if the well-known chemical gradient in TMC-1 is reflected in the amount of rudimentary forms of carbon available in the gas-phase. As a tracer we use the CH radical which is supposed to be well correlated with carbon atoms and simple hydrocarbon ions. Methods. We observed the 9-cm Λ-doubling lines of CH along the dense filament of TMC-1. The CH column densities were compared with the total H 2 column densities derived using the 2MASS NIR data and previously published SCUBA maps and with OH column densities derived using previous observations with Effelsberg. We also modelled the chemical evolution of TMC-1 adopting physical conditions typical of dark clouds using the UMIST Database for Astrochemistry gas-phase reaction network to aid the interpretation of the observed OH/CH abundance ratios. Results. The CH column density has a clear peak in the vicinity of the cyanopolyyne maximum of TMC-1. The fractional CH abundance relative to H 2 increases steadily from the northwestern end of the filament where it lies around 1.0 × 10 −8 , to the southeast where it reaches a value of 2.0 × 10 −8 . The OH and CH column densities are well correlated, and we obtained OH/CH abundance ratios of ∼16-20. These values are clearly larger than what has been measured recently in diffuse interstellar gas and is likely to be related to C to CO conversion at higher densities. The good correlation between CH and OH can be explained by similar production and destruction pathways. We suggest that the observed CH and OH abundance gradients are mainly due to enhanced abundances in a low-density envelope which becomes more prominent in the southeastern part and seems to continue beyond the dense filament.Conclusions. An extensive envelope probably signifies an early stage of dynamical evolution, and conforms with the detection of a large CH abundance in the southeastern part of the cloud. The implied presence of other simple forms of carbon in the gas phase provides a natural explanation for the observation of "early-type" molecules in this region.

Context. Mass estimates of interstellar clouds from far-infrared and submillimetre mappings depend on the assumed dust absorption cross-section for radiation at those wavelengths. Aims. The aim is to determine the far-IR dust absorption cross-section in a starless, dense core located in Corona Australis. The value is needed for determining of the core mass and other physical properties. It can also have a bearing on the evolutionary stage of the core. Methods. We correlated near-infrared stellar H − K s colour excesses of background stars from NTT/SOFI with the far-IR optical depth map, τ FIR , derived from Herschel 160, 250, 350, and 500 μm data. The Herschel maps were also used to construct a model for the cloud to examine the effect of temperature gradients on the estimated optical depths and dust absorption cross-sections. Results. A linear correlation is seen between the colour H − K s and τ FIR up to high extinctions (A V ∼ 25). The correlation translates to the average extinction ratio A 250 μm /A J = 0.0014 ± 0.0002, assuming a standard near-infrared extinction law and a dust emissivity index β = 2. Using an empirical N H /A J ratio we obtain an average absorption cross-section per H nucleus of σ H 250 μm = (1.8 ± 0.3) × 10 −25 cm 2 H-atom −1 , corresponding to a cross-section per unit mass of gas κ g 250 μm = 0.08 ± 0.01 cm 2 g −1 . 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 τ FIR correctly, we find that the relationship between H − K s and τ FIR agrees with the recently determined relationship between σ H and N H in Orion A. Conclusions. 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 being 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.

Context. Dust grains play an important role in the synthesis of molecules in the interstellar medium, from the simplest species, such as H2, to complex organic molecules. How some of these solid-state molecules are converted into gas-phase species is still a matter of debate. Aims. Our aim is to directly compare ice and gas abundances of methanol (CH3OH) and carbon monoxide (CO) obtained from near-infrared (2.5−5 μm) and millimetre (1.3 mm) observations and to investigate the relationship between ice, dust, and gas in low-mass protostellar envelopes. Methods. We present Submillimeter Array (SMA) and Atacama Pathfinder EXperiment (APEX) observations of gas-phase CH3OH (JK = 5K−4K), 13CO, and C18O (J = 2−1) towards the multiple protostellar system IRAS 05417+0907, which is located in the B35A cloud, λ Orionis region. We use archival IRAM 30 m data and AKARI H2O, CO, and CH3OH ice observations towards the same target to compare ice and gas abundances and directly calculate CH3OH and CO gas-to-ice ratios. Results. The CO isotopologue emissions are extended, whereas the CH3OH emission is compact and traces the giant molecular outflow emanating from IRAS 05417+0907. A discrepancy between sub-millimetre dust emission and H2O ice column density is found for B35A−4 and B35A−5, similar to what has previously been reported. B35A−2 and B35A−3 are located where the sub-millimetre dust emission peaks and show H2O column densities lower than that of B35A−4. Conclusions. The difference between the sub-millimetre continuum emission and the infrared H2O ice observations suggests that the distributions of dust and H2O ice differ around the young stellar objects in this dense cloud. The reason for this may be that the four sources are located in different environments resolved by the interferometric observations: B35A−2, B35A−3, and, in particular, B35A−5 are situated in a shocked region that is plausibly affected by sputtering and heating, which in turn impacts the sub-millimetre dust emission pattern, while B35A−4 is situated in a more quiescent part of the cloud. Gas and ice maps are essential for connecting small-scale variations in the ice composition with the large-scale astrophysical phenomena probed by gas observations.