The CN/C15 N isotopic ratio towards dark clouds

Abstract

Understanding the origin of the composition of solar system cosmomaterials is a central question, not only in the cosmochemistry and astrochemistry fields, and requires various approaches to be combined. Measurements of isotopic ratios in cometary materials provide strong constraints on the content of the protosolar nebula. Their relation with the composition of the parental dark clouds is, however, still very elusive. In this paper, we bring new constraints based on the isotopic composition of nitrogen in dark clouds, with the aim of understanding the chemical processes that are responsible for the observed isotopic ratios. We have observed and detected the fundamental rotational transition of C${}^{15}$N towards two starless dark clouds, L1544 and L1498. We were able to derive the column density ratio of C${}^{15}$N over ${}^{13}$CN towards the same clouds, and obtain the CN/C${}^{15}$N isotopic ratios, which were found to be $500\pm 75$ for both L1544 and L1498. These values are therefore marginally consistent with the protosolar value of 441. Moreover, this ratio is larger than the isotopic ratio of nitrogen measured in HCN. In addition, we present model calculations of the chemical fractionation of nitrogen in dark clouds, which make it possible to understand how CN can be deprived of ${}^{15}$N and HCN can simultaneously be enriched in heavy nitrogen. The non-fractionation of N2H+, however, remains an open issue and we propose some chemical way of alleviating the discrepancy between model predictions and the observed ratios.

Accepted for publication in A&A

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Cited by in corpus (31)

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• The chemical inventory of the planet-hosting disk PDS 70
• Direct evidence of multiple reservoirs of volatile nitrogen in a protosolar nebula analogue
• Nitrogen fractionation in high-mass star-forming cores across the Galaxy
• Carbon isotopic fractionation in molecular clouds
• Nitrogen Fractionation in Protoplanetary Disks from the H13CN/HC15N Ratio
• Nitrogen and hydrogen fractionation in high-mass star forming cores from observations of HCN and HNC
• Observations of nitrogen isotope fractionation in deeply embedded protostars
• Revised Models of Interstellar Nitrogen Isotopic Fractionation
• Depletion of heavy nitrogen in the cold gas of star-forming regions
• First measurements of 15N fractionation in N2H+ toward high-mass star forming cores
• Abundance of HCN and its C and N isotopologues in L1498
• Gas-grain model of carbon fractionation in dense molecular clouds
• The nitrogen isotopic ratio of HC3N towards the L1544 prestellar core
• An unbiased spectral line survey observation toward the low-mass star-forming region L1527
• The C${}^{14}$N/C${}^{15}$N Ratio in Diffuse Molecular Clouds
• N${}_2$H${}^{+}$ and N${}^{15}$NH${}^{+}$ towards the prestellar core 16293E in L1689N
• First interferometric study of enhanced N-fractionation in N${}_2$H${}^{+}$: the high-mass star-forming region IRAS 05358+3543
• ALMA Autocorrelation Spectroscopy of Comets: The HCN/H^13CN ratio in C/2012 S1 (ISON)
• Depletion and fractionation of nitrogen in collapsing cores
• CHEMOUT: CHEMical complexity in star-forming regions of the OUTer Galaxy III. Nitrogen isotopic ratios in the outer Galaxy
• Nitrogen fractionation towards a pre-stellar core traces isotope-selective photodissociation
• Probing the kinematics and chemistry of the hot core Mon R 2 IRS 3 using ALMA observations
• Tracing Molecular Stratification within an Edge-on Protoplanetary Disk
• First sample of ${\mathrm{N}}_2{\mathrm{H}}^{+}$ nitrogen isotopic ratio measurements in low-mass protostars
• Depletion of 15N in the center of L1544: Early transition from atomic to molecular nitrogen?
• ALMA-IRDC II. First high-angular resolution measurements of the 14N/15N ratio in a large sample of infrared-dark cloud cores
• Spin-orbit transitions in the N${}^{+}$(${}^3{P}_{J_A}$) + H${}_2$ $\to$ NH${}^{+}$($X^2\Pi$, ${}^4{\Sigma }^{-}$)+ H(${}^{2}S$) reaction, using adiabatic and mixed quantum-adiabatic statistical approaches
• Hyperfine transitions of 13CN from pre-protostellar sources