Mon. Not. R. Astron. Soc., 476, 1982-1990 (2018/May-2)
Deuterium and 15N fractionation in N2H+ during the formation of a Sun-like star.
DE SIMONE M., FONTANI F., CODELLA C., CECCARELLI C., LEFLOCH B., BACHILLER R., LOPEZ-SEPULCRE A., CAUX E., VASTEL C. and SOLDATESCHI J.
Abstract (from CDS):
Although chemical models predict that the deuterium fractionation in N2H+ is a good evolutionary tracer in the star formation process, the fractionation of nitrogen is still a poorly understood process. Recent models have questioned the similar evolutionary trend expected for the two fractionation mechanisms in N2H+, based on a classical scenario in which ion-neutral reactions occurring in cold gas should have caused an enhancement of the abundance of N2D^+, 15NNH+^, and N15NH+. In the framework of the ASAI IRAM-30m large program, we have investigated the fractionation of deuterium and 15N in N2H+ in the best known representatives of the different evolutionary stages of the Sun-like star formation process. The goal is to ultimately confirm (or deny) the classical 'ion-neutral reactions' scenario that predicts a similar trend for D and 15N fractionation. We do not find any evolutionary trend of the 14N/15N ratio from both the 15NNH+ and N15NH+ isotopologues. Therefore, our findings confirm that, during the formation of a Sun-like star, the core evolution is irrelevant in the fractionation of 15N. The independence of the 14N/15N ratio with time, found also in high-mass star-forming cores, indicates that the enrichment in 15N revealed in comets and protoplanetary discs is unlikely to happen at core scales. Nevertheless, we have firmly confirmed the evolutionary trend expected for the H/D ratio, with the N2H+/N2D+ ratio decreasing before the pre-stellar core phase, and increasing monotonically during the protostellar phase. We have also confirmed clearly that the two fractionation mechanisms are not related.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
stars: formation - ISM: clouds - ISM: molecules - radio lines: ISM
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