Gas-phase Elemental abundances in Molecular cloudS (GEMS) XI. The evolution of HCN, HNC, and N2H+ isotopic ratios in starless cores

Abstract

Isotopic ratios have been used as chemical diagnostics to investigate the origin of the material in the Solar System. We have determined the HCN, HNC, and N2H+ isotopic ratios and the chemical age in a large sample of 23 starless cores located in different environments. This work uses IRAM 30m data to constrain the D/H ratio of HCN, HNC, and N2H+ as well as the 14N/15N ratio of HCN and HNC. The observed abundances have been modeled using the chemical code DNAUTILUS 2.0. Deuterated compounds are detected in all of our sample cores, with average DNC/HNC, DCN/HCN, and N2D+/N2H+ values of 0.054$\pm$0.019, 0.036$\pm$0.033, and 0.15$\pm$0.11, respectively. The deuterium fractions (Dfrac) show a weak correlation with temperature and a large scatter that reflects that other factors such as core evolution could also play a significant role. Our chemical model is able to reproduce all the observed values with 0.2-0.3 Myr in Taurus and 0.3-0.5 Myr in Perseus and Orion. The 14N/15N isotopic ratio is found to be different between HCN/HC15N (430$\pm$120) and HNC/H15NC (296$\pm$64). We find no correlation between these ratios and the deuterium fractions, but we report a weak correlation with temperature. The Dfrac of HCN, HNC, and N2H+ can be used as evolutionary tracers of starless cores as long as the physical parameters are well constrained. The HCN/HC15N and HNC/H15NC ratios are not correlated with Dfrac, suggesting that the detected variations are not correlated with the core evolutionary stage. The average value of the HCN/HC15N ratio in our sample is significantly higher than the values measured in protostars and protoplanetary disks, possibly indicating that nitrogen fractionation processes are taking place during the protostellar phase.

arXiv commentAccepted for publication in Astronomy and Astrophysics: 22 pages, 17 figures

References in corpus (68)

• An atomic and molecular database for analysis of submillimetre line observations
• From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey
• The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual Atomic and Molecular Data Centre, VAMDC
• Herschel view of the Taurus B211/3 filament and striations: Evidence of filamentary growth?
• Our astrochemical heritage
• Large-Scale Structure of the Molecular Gas in Taurus Revealed by High Linear Dynamic Range Spectral Line Mapping
• Chemodynamical evolution of the Milky Way disk I: The solar vicinity
• Probing the evolutionary status of starless cores through N2H+ and N2D+ observations
• Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurus region
• Molecular ions in L1544. II. The ionization degree
• Cosmic-ray ionization of molecular clouds
• Observing the gas temperature drop in the high-density nucleus of L 1544
• A Large Catalog of Accurate Distances to Local Molecular Clouds: The Gaia DR2 Edition
• Detection of doubly-deuterated methanol in the solar-type protostar IRAS16293-2422
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• On the internal structure of starless cores. II. A molecular survey of L1498 and L1517B
• CO Depletion and Deuterium Fractionation in Prestellar Cores
• Chemical modeling of L183 (= L134N) : an estimate of the ortho/para H2 ratio
• The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars
• Isotopic fractionation of carbon, deuterium and nitrogen : a full chemical study
• Gas phase Elemental abundances in Molecular cloudS (GEMS) I. The prototypical dark cloud TMC 1
• Large excess of heavy nitrogen in both hydrogen cyanide and cyanogen from comet 17P/Holmes
• HCN/HNC intensity ratio: a new chemical thermometer for the molecular ISM
• Nitrogen isotopic ratios in Barnard 1: a consistent study of the N2H+, NH3, CN, HCN and HNC isotopologues
• IN-SYNC II: Virial Stars from Sub-Virial Cores -- The Velocity Dispersion of Embedded Pre-Main-Sequence Stars in NGC 1333
• The 15N-enrichment in dark clouds and Solar System objects
• New extended deuterium fractionation model: assessment at dense ISM conditions and sensitivity analysis
• Nitrogen superfractionation in dense cloud cores
• Nitrogen hydrides and the H2 ortho-to-para ratio in dark clouds
• Deuterium chemistry in the Orion Bar PDR - "warm" chemistry starring CH2D+
• Profiling filaments: comparing near-infrared extinction and submillimetre data in TMC-1
• Deuterated molecules as a probe of ionization fraction in dense interstellar clouds
• Detection of (15)NNH+ in L1544: non-LTE modelling of dyazenilium hyperfine line emission and accurate (14)N/(15)N values
• Herschel-Planck dust optical depth and column density maps - II. Perseus
• Gas phase Elemental abundances in Molecular cloudS (GEMS) VII. Sulfur elemental abundance
• Sensitivity analyses of dense cloud chemical models
• Ionization fraction and the enhanced sulfur chemistry in Barnard 1
• Direct evidence of multiple reservoirs of volatile nitrogen in a protosolar nebula analogue
• DCO${}^{+}$, DCN and N${}_2$D${}^{+}$ reveal three different deuteration regimes in the disk around the Herbig Ae star HD163296
• Nitrogen fractionation in high-mass star-forming cores across the Galaxy
• Nitrogen Fractionation in Protoplanetary Disks from the H13CN/HC15N Ratio
• Observations of nitrogen isotope fractionation in deeply embedded protostars
• Nitrogen and hydrogen fractionation in high-mass star forming cores from observations of HCN and HNC
• Gas phase Elemental abundances in Molecular cloudS (GEMS). IV. Observational results and statistical trends
• Properties of Starless and Prestellar Cores in Taurus Revealed by Herschel SPIRE/PACS Imaging
• Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation
• Radial Migration of the Sun in the Milky Way: a Statistical Study
• Deuterium Fractionation: the Ariadne's Thread from the Pre-collapse Phase to Meteorites and Comets today
• First measurements of 15N fractionation in N2H+ toward high-mass star forming cores
• A combined IRAM and Herschel/HIFI study of cyano(di)acetylene in Orion KL: tentative detection of DC3N
• Hydrodynamics with gas-grain chemistry and radiative transfer: comparing dynamical and static models
• Abundance of HCN and its C and N isotopologues in L1498
• Gas-grain model of carbon fractionation in dense molecular clouds
• An unbiased spectral line survey observation toward the low-mass star-forming region L1527
• A Survey of CH2DOH Towards Starless and Prestellar Cores in the Taurus Molecular Cloud
• First measurement of the 14N/15N ratio in the analogue of the Sun progenitor OMC-2 FIR4
• Evolutionary view through the starless cores in Taurus: deuteration in TMC 1-C and TMC 1-CP
• First detection of NHD and ND${}_2$ in the interstellar medium
• Gas phase Elemental abundances in Molecular cloudS (GEMS) VI. A sulphur journey across star-forming regions: study of thioformaldehyde emission
• An efficient method for determining the chemical evolution of gravitationally collapsing prestellar cores
• Depletion and fractionation of nitrogen in collapsing cores
• Combined model for ${}^{15}\mathrm{N}$, ${}^{13}\mathrm{C}$, and spin-state chemistry in molecular clouds
• Linking the dust and chemical evolution: Taurus and Perseus -- New collisional rates for HCN, HNC, and their C, N, and H isotopologues
• Similar levels of deuteration in the pre-stellar core L1544 and the protostellar core HH211
• Nitrogen fractionation towards a pre-stellar core traces isotope-selective photodissociation
• CS Depletion in Prestellar Cores
• Chemical compositions of five Planck cold clumps
• Gas phase Elemental abundances in Molecular cloudS (GEMS). IX. Deuterated compounds of H2S in starless cores

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• An 18 - 25 GHz spectroscopic survey of southern hemisphere dense cores