Imaging the water snowline in protostellar envelopes

Abstract

AbstractDetermining the locations of the major snowlines in protostellar environments is crucial to fully understand the planet formation process and its outcome. Despite being located far enough from the central star to be spatially resolved with ALMA, the CO snowline remains difficult to detect directly in protoplanetary disks. Instead, its location can be derived from N2H+emission, when chemical effects like photodissociation of CO and N2are taken into account. The water snowline is even harder to observe than that for CO, because in disks it is located only a few AU from the protostar, and from the ground only the less abundant isotopologue H218O can be observed. Therefore, using an indirect chemical tracer, as done for CO, may be the best way to locate the water snowline. A good candidate tracer is HCO+, which is expected to be particularly abundant when its main destructor, H2O, is frozen out. Comparison of H218O and H13CO+emission toward the envelope of the Class 0 protostar IRAS2A shows that the emission from both molecules is spatially anticorrelated, providing a proof of concept that H13CO+can indeed be used to trace the water snowline in systems where it cannot be imaged directly.