Nitrogen Isotopic Fractionation in Interstellar Ammonia

International audienceUsing the Green Bank Telescope, we have obtained accurate measurements of the 14N/15N isotopic ratio in ammonia in two nearby cold, dense molecular clouds, Barnard 1 and NGC 1333. The 14N/15N ratio in Barnard 1, 334 ± 50 (3sigma), is particularly well constrained and falls in between the local interstellar medium/proto-solar value of ~450 and the terrestrial atmospheric value of 272. The NGC 1333 measurement is consistent with the Barnard 1 result, but has a larger uncertainty. We do not see evidence for the very high 15N enhancements seen in cometary CN. Sensitive observations of a larger, carefully selected sample of prestellar cores with varying temperatures and gas densities can significantly improve our understanding of the nitrogen fractionation in the local interstellar medium and its relation to the isotopic ratios measured in various solar system reservoirs