First Measurements of 15N Fractionation in N2H+ toward High-mass Star-forming Cores
Abstract
We report on the first measurements of the isotopic ratio 14N/15N in N2H+ toward a statistically significant sample of high-mass star-forming cores. The sources belong to the three main evolutionary categories of the high-mass star formation process: high-mass starless cores, high-mass protostellar objects, and ultracompact H ii regions. Simultaneous measurements of the 14N/15N ratio in CN have been made. The 14N/15N ratios derived from N2H+ show a large spread (from ∼180 up to ∼1300), while those derived from CN are in between the value measured in the terrestrial atmosphere (∼270) and that of the proto-solar nebula (∼440) for the large majority of the sources within the errors. However, this different spread might be due to the fact that the sources detected in the N2H+ isotopologues are more than those detected in the CN ones. The 14N/15N ratio does not change significantly with the source evolutionary stage, which indicates that time seems to be irrelevant for the fractionation of nitrogen. We also find a possible anticorrelation between the 14N/15N (as derived from N2H+) and the H/D isotopic ratios. This suggests that 15N enrichment could not be linked to the parameters that cause D enrichment, in agreement with the prediction by recent chemical models. These models, however, are not able to reproduce the observed large spread in 14N/15N, pointing out that some important routes of nitrogen fractionation could be still missing in the models.
Based on observations carried out with the IRAM-30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).- Publication:
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The Astrophysical Journal
- Pub Date:
- August 2015
- DOI:
- 10.1088/2041-8205/808/2/L46
- arXiv:
- arXiv:1506.05180
- Bibcode:
- 2015ApJ...808L..46F
- Keywords:
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- ISM: molecules;
- molecular data;
- radio lines: ISM;
- stars: formation;
- submillimeter: ISM;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 2 Figures, accepted for publication in ApJL