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Nitrogen fractionation is commonly used to assess the thermal history ofSolar System volatiles. With ALMA it is for the first time possible to directlymeasure 14N/15N ratios in common molecules during the assembly of planetarysystems. We present ALMA observations of the H13CN and HC15N J=3-2 lines at0".5 angular resolution, toward a sample of six protoplanetary disks, selectedto span a range of stellar and disk structure properties. Adopting a typical12C/13C ratio of 70, we find comet-like 14N/15N ratios of 80-160 in 5/6 of thedisks (3 T Tauri and 2 Herbig Ae disks) and lack constraints for one of the TTauri disks (IM Lup). There are no systematic differences between T Tauri andHerbig Ae disks, or between full and transition disks within the sample. Inaddition, no correlation is observed between disk-averaged D/H and 14N/15Nratios in the sample. One of the disks, V4046 Sgr, presents unusually brightHCN isotopologue emission, enabling us to model the radial profiles of H13CNand HC15N. We find tentative evidence of an increasing 14N/15N ratio withradius, indicating that selective photodissociation in the inner disk isimportant in setting the 14N/15N ratio during planet formation.

Nitrogen Fractionation in Protoplanetary Disks from the H13CN/HC15N Ratio