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We investigate the delivery of regular and deuterated forms of water fromprestellar cores to circumstellar disks. We adopt a semi-analyticalaxisymmetric two-dimensional collapsing core model with post-processing gas-iceastrochemical simulations, in which a layered ice structure is considered. Thephysical and chemical evolutions are followed until the end of the mainaccretion phase. When mass averaged over the whole disk, a forming disk has asimilar H2O abundance and HDO/H2O abundance ratio as their precollapse values(within a factor of 2), regardless of time in our models. Consistent withprevious studies, our models suggest that interstellar water ice is deliveredto forming disks without significant alteration. On the other hand, the localvertically averaged H2O ice abundance and HDO/H2O ice ratio can differ more, byup to a factor of several, depending on time and distance from a central star.Key parameters for the local variations are the fluence of stellar UV photonsen route into the disk and the ice layered structure, the latter of which ismostly established in the prestellar stages. We also find that even ifinterstellar water ice is destroyed by stellar UV and (partly) reformed priorto disk entry, the HDO/H2O ratio in reformed water ice is similar to theoriginal value. This finding indicates that some caution is needed indiscussions on the prestellar inheritance of H2O based on comparisons betweenthe observationally derived HDO/H2O ratio in clouds/cores and that indisks/comets. Alternatively, we propose that the ratio of D2O/HDO to HDO/H2Obetter probes the prestellar inheritance of H2O. It is also found that icyorganics are more enriched in deuterium than water ice in forming disks. Thedifferential deuterium fractionation in water and organics is inherited fromthe prestellar stages.

Water delivery from cores to disks: deuteration as a probe of the prestellar inheritance of H2O