Context. Although deuterium enrichment of water may provide an essential piece of information in the understanding of the formation of comets and protoplanetary systems, only a few studies up to now have aimed at deriving the HDO/H 2 O ratio in low-mass star forming regions. Previous studies of the molecular deuteration toward the solar-type class 0 protostar, IRAS 16293-2422, have shown that the D/H ratio of water is significantly lower than other grain-surface-formed molecules. It is not clear if this property is general or particular to this source. Aims. In order to see if the results toward IRAS 16293−2422 are particular, we aimed at studying water deuterium fractionation in a second low-mass solar-type protostar, NGC1333-IRAS2A. Methods. Using the 1-D radiative transfer code RATRAN, we analyzed five HDO transitions observed with the IRAM 30 m, JCMT, and APEX telescopes. We assumed that the abundance profile of HDO in the envelope is a step function, with two different values in the inner warm (T > 100 K) and outer cold (T < 100 K) regions of the protostellar envelope. Results. The inner and outer abundance of HDO is found to be well constrained at the 3σ level. The obtained HDO inner and outer fractional abundances are x HDO in = 6.6 × 10 −8 -1.0 × 10 −7 (3σ) and x HDO out = 9 × 10 −11 -1.8 × 10 −9 (3σ). These values are close to those in IRAS 16293-2422, which suggests that HDO may be formed by the same mechanisms in these two solar-type protostars. Taking into account the (rather poorly onstrained) H 2 O abundance profile deduced from Herschel observations, the derived HDO/H 2 O in the inner envelope is ≥1% and in the outer envelope it is 0.9%-18%. These values are more than one order of magnitude higher than what is measured in comets. If the same ratios apply to the protosolar nebula, this would imply that there is some efficient reprocessing of the material between the protostellar and cometary phases. Conclusions. The H 2 O inner fractional abundance could be further constrained by an analysis of newer observations of high-energy H 18 2 O lines. These new observations would be required to understand water fractionation in more detail.

Context. Water is an essential molecule in oxygen chemistry and the main constituent of grain icy mantles. The formation of water can be studied through the HDO/H 2 O ratio. Thanks to the launch of the Herschel satellite and the advance of sensitive submillimeter receivers on ground telescopes, many H 2 O and HDO transitions can now be observed, enabling more accurate studies of the level of water fractionation. Aims. Using these new technologies, we aim at revisiting the water fractionation studies toward massive star-forming regions. We present here a detailed study toward G34.26+0.15, a massive star-forming region associated with compact HII regions. Methods. We present observations of five HDO lines obtained with the APEX telescope. Two of those transitions are ground-state transitions. Two of the three high-excitation lines were additionally observed at higher angular resolution with the SMA. We analyzed these observations using the 1D radiative transfer code RATRAN and adopting different physical profiles from two different models. Results. Although the inner and outer fractional abundances relative to H 2 can be best constrained to be X HDO in (T > 100 K) = (5−7) × 10 −8 (3σ) and X HDO out (T ≤ 100 K) = (0.3−2) × 10 −11 (3σ), the line profile of the 893 GHz ground transition cannot be well reproduced. This line profile is shown to be very sensitive to the velocity field. To better constrain the velocity field, it is necessary to observe the HDO line at 893 GHz with high angular resolution. The H 2 O abundance is deduced from one high-excitation and one ground transition H 18 2 O line. The D/H ratios of water are 3.0 × 10 −4 in the inner region and (1.9−4.9) × 10 −4 in the outer region of the core. The HDO fractional abundance in the inner and outer regions are different by more than four orders, which implies that the sublimation is very similar in low-and high-mass protostars. The D/H ratios of water in G34.26 + 0.15 are close to the value obtained for the same source in a previous study, and similar to those in other high-mass sources, but lower than those in low-mass protostars, suggesting the possibility that the dense and cold pre-collapse phase is shorter for high-mass star-forming regions.