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|Title:||Deuterium and 15N fractionation in N2H+ during the formation of a Sun-like star||Authors:||De Simone, M.
|Issue Date:||2018||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||476||Issue:||2||First Page:||1982||Abstract:||Although chemical models predict that the deuterium fractionation in N<SUB>2</SUB>H<SUP>+</SUP> 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 N<SUB>2</SUB>H<SUP>+</SUP>, based on a classical scenario in which ion-neutral reactions occurring in cold gas should have caused an enhancement of the abundance of N<SUB>2</SUB>D<SUP>+, 15</SUP>NNH<SUP>+</SUP>, and N<SUP>15</SUP>NH<SUP>+</SUP>. In the framework of the ASAI IRAM-30m large program, we have investigated the fractionation of deuterium and <SUP>15</SUP>N in N<SUB>2</SUB>H<SUP>+</SUP> 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 <SUP>15</SUP>N fractionation. We do not find any evolutionary trend of the <SUP>14</SUP>N/<SUP>15</SUP>N ratio from both the <SUP>15</SUP>NNH<SUP>+</SUP> and N<SUP>15</SUP>NH<SUP>+</SUP> isotopologues. Therefore, our findings confirm that, during the formation of a Sun-like star, the core evolution is irrelevant in the fractionation of <SUP>15</SUP>N. The independence of the <SUP>14</SUP>N/<SUP>15</SUP>N ratio with time, found also in high-mass star-forming cores, indicates that the enrichment in <SUP>15</SUP>N 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 N<SUB>2</SUB>H<SUP>+</SUP>/N<SUB>2</SUB>D<SUP>+</SUP> 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.||URI:||http://hdl.handle.net/20.500.12386/27814||URL:||https://academic.oup.com/mnras/article/476/2/1982/4848314||ISSN:||0035-8711||DOI:||10.1093/mnras/sty353||Bibcode ADS:||2018MNRAS.476.1982D||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Oct 27, 2020
checked on Oct 27, 2020
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