First measurement of the 14N/15N ratio in the analogue of the Sun
  progenitor OMC-2 FIR4
  We present a complete census of the 14N/15N isotopic ratio in the most
abundant N-bearing molecules towards the cold envelope of the protocluster
OMC-2 FIR4, the best known Sun progenitor. To this scope, we analysed the
unbiased spectral survey obtained with the IRAM-30m telescope at 3mm, 2mm and
1mm. We detected several lines of CN, HCN, HNC, HC3N, N2H+, and their
respective 13C and 15N isotopologues. The lines relative fluxes are compatible
with LTE conditions and moderate line opacities have been corrected via a
Population Diagram method or theoretical relative intensity ratios of the
hyperfine structures. The five species lead to very similar 14N/15N isotopic
ratios, without any systematic difference between amine and nitrile bearing
species as previously found in other protostellar sources. The weighted average
of the 14N/15N isotopic ratio is 270 +/- 30. This 14N/15N value is remarkably
consistent with the [250-350] range measured for the local galactic ratio but
significantly differs from the ratio measured in comets (around 140).
High-angular resolution observations are needed to examine whether this
discrepancy is maintained at smaller scales. In addition, using the CN, HCN and
HC3N lines, we derived a 12C/13C isotopic ratio of 50 +/- 5.
