NGC1333-IRAS2A water snowline imaging

NGC1333-IRAS2A was observed using NOEMA at ~0.9 arcsec resolution, targeting the H^13^CO^+^ J=3-2 transition at 260.255GHz. The integrated emission profile was analyzed using 1D radiative transfer modeling of a spherical envelope with a parametrized abundance profile for H^13^CO^+^. This profile was validated with a full chemical model.

The H^13^CO^+^ emission peaks ~2-arcsec northeast of the continuum peak, whereas H_2_^18^O shows compact emission on source. Quantitative modeling shows that a decrease in H13CO+ abundance by at least a factor of six is needed in the inner ~360AU to reproduce the observed emission profile. Chemical modeling predicts indeed a steep increase in HCO^+^ just outside the water snowline; the 50% decrease in gaseous H_2_O at the snowline is not enough to allow HCO^+^ to be abundant.

This places the water snowline at 225AU, further away from the star than expected based on the 1D envelope temperature structure for NGC1333-IRAS2A. In contrast, DCO^+^ observations show that the CO snowline is at the expected location, making an outburst scenario unlikely. The spatial anticorrelation of the H^13^CO^+^ and H_2_^18^O emission provide a proof of concept that H^13^CO^+^ can be used as a tracer of the water snowline.