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We present a complete census of the 14N/15N isotopic ratio in the mostabundant N-bearing molecules towards the cold envelope of the protoclusterOMC-2 FIR4, the best known Sun progenitor. To this scope, we analysed theunbiased spectral survey obtained with the IRAM-30m telescope at 3mm, 2mm and1mm. We detected several lines of CN, HCN, HNC, HC3N, N2H+, and theirrespective 13C and 15N isotopologues. The lines relative fluxes are compatiblewith LTE conditions and moderate line opacities have been corrected via aPopulation Diagram method or theoretical relative intensity ratios of thehyperfine structures. The five species lead to very similar 14N/15N isotopicratios, without any systematic difference between amine and nitrile bearingspecies as previously found in other protostellar sources. The weighted averageof the 14N/15N isotopic ratio is 270 +/- 30. This 14N/15N value is remarkablyconsistent with the [250-350] range measured for the local galactic ratio butsignificantly differs from the ratio measured in comets (around 140).High-angular resolution observations are needed to examine whether thisdiscrepancy is maintained at smaller scales. In addition, using the CN, HCN andHC3N lines, we derived a 12C/13C isotopic ratio of 50 +/- 5.

First measurement of the 14N/15N ratio in the analogue of the Sun progenitor OMC-2 FIR4