The origin of the heavily fractionated reservoir of nitrogen in comets remains an issue in the theory of their formation and hence of the solar system. Whether the fractionated reservoir traced by comets is inherited from the interstellar cloud or is the product of processes taking place in the protostar, or in the protoplanetary disk, remains unclear. So far, observations of nitrogen isotopic ratios in protostars or prestellar cores have not securely identified such a fractionated reservoir owing to the intrinsic difficulty of direct isotopic ratios measurements. In this article, we report the detection of 5 rotational lines of \ce{HC3N}, {including the weaker components of the hyperfine multiplets}, and two rotational lines of its $^{15}$N isotopologue, towards the L1544 prestellar core. Based on a MCMC/non-LTE multi-line analysis at the hyperfine level, we derive the column densities of \ce{HC3N} ($8.0\pm0.4\tdix{13}$\cc) and \ce{HC3^{15}N} ($2.0\pm0.4\tdix{11}$\cc) and derive an isotopic ratio of 400$\pm$20(1$σ$). This value suggests that \ce{HC3N} is slightly depleted in $^{15}$N in L1544 with respect to the elemental $^{14}$N/$^{15}$N ratio {of $\approx$330} in the present-day local interstellar medium. Our study also stresses the need for radiative calculations at the hyperfine level. Finally, the comparison of the derived ratio with those obtained in CN and HCN in the same core seems to favor CN+C$_2$H$_2$ as the dominant formation route to HC$_3$N. However, uncertainties in the isotopic ratios preclude definitive conclusions.
Using the Green Bank Telescope (GBT), we have obtained accurate measurements of the $^{14}$N/$^{15}$N isotopic ratio in ammonia in two nearby cold, dense molecular clouds, Barnard~1 and NGC 1333. The $^{14}$N/$^{15}$N ratio in Barnard~1, $334 \pm 50$ (3$σ$), is particularly well constrained and falls in between the local interstellar medium/proto-solar value of $\sim 450$ and the terrestrial atmospheric value of 272. The NGC 1333 measurement is consistent with the Barnard~1 result, but has a larger uncertainty. We do not see evidence for the very high $^{15}$N enhancements seen in cometary CN.…
The line intensities of the fundamental rotational transitions of H13CN and HC15N were observed towards two prestellar cores, L183 and L1544, and lead to molecular isotopic ratios 140 6 14N/15N 6 250 and 140 6 14N/15N 6 360, respectively. The range of values reflect genuine spatial variations within the cores. A comprehensive analysis of the available measurements of the nitrogen isotopic ratio in prestellar cores show that molecules carrying the nitrile functional group appear to be systematically 15N-enriched com- pared to those carrying the amine functional group. A chemical origin for the …
The isotopic ratio of nitrogen measured in primitive Solar System bodies shows a broad range of values, the origin of which remains unknown. One key question is whether these isotopic reservoirs of nitrogen predate the comet formation stage or are posterior to it. Another central question is elucidating the processes that can produce the observed variations in the 14N/15N isotopic ratio. Disks that orbit pre-main-sequence stars provide unique opportunities for observing the chemical content of analogs of the protosolar nebula and therefore for building a comprehensive scenario for the origin o…
Measurements of the nitrogen isotopic ratio in Solar System comets show a constant value, ~140, which is three times lower than the protosolar ratio, a highly significant difference that remains unexplained. Observations of static starless cores at early stages of collapse confirm the theoretical expectation that nitrogen fractionation in interstellar conditions is marginal for most species. Yet, observed isotopic ratios in N2H+ are at variance with model predictions. These gaps in our understanding of how the isotopic reservoirs of nitrogen evolve, from interstellar clouds to comets, and, mor…
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 f…
Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of $^{15}$N enrichments found in comets and meteorites. Chemical model calculations indicate that atom-molecular ion and ion-molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense cloud chemistry show that the revised $^{15}$N enrichments fail to match observed v…
Context. The nitrogen isotopic ratio is considered an important diagnostic tool of the star formation process, and $N_2H^+$ is particularly important because it is directly linked to molecular nitrogen $N_2$. However, theoretical models still lack to provide an exhaustive explanation for the observed $^{14}N/^{15}N$ values. Aims. Recent theoretical works suggest that the $^{14}N/^{15}N$ behaviour is dominated by two competing reactions that destroy $ N_2H^+$: dissociative recombination and reaction with CO. When CO is depleted from the gas phase, if $N_2H^+$ recombination rate is lower with re…
Context. The increased sensitivity and high spectral resolution of millimeter telescopes allow the detection of an increasing number of isotopically substituted molecules in the interstellar medium. The 14N/ 15N ratio is difficult to measure directly for carbon containing molecules. Aims. We want to check the underlying hypothesis that the 13C/ 12C ratio of nitriles and isonitriles is equal to the elemental value via a chemical time dependent gas phase chemical model. Methods. We have built a chemical network containing D, 13C and 15N molecular species after a careful check of the possible fra…
Isotopic ratios are keys to understanding the origin and early evolution of the solar system in the context of Galactic nucleosynthesis. The large range of measured $^{14}$N/$^{15}$N isotopic ratios in the solar system reflects distinct reservoirs of nitrogen whose origins remain to be determined. We have directly measured a C$^{14}$N/C$^{15}$N abundance ratio of 323$\pm$30 in the disk orbiting the nearby young star TW Hya. This value, which is in good agreement with nitrogen isotopic ratios measured for prestellar cores, likely reflects the primary present-day reservoir of nitrogen in the sol…
High degrees of deuterium fractionation are commonly found in cold prestellar cores and in the envelopes around young protostars. As it brings strong constraints to chemical models, deuterium chemistry is often used to infer core history or molecule formation pathways. Whereas a large number of observations is available regarding interstellar deuterated stable molecules, relatively little is known about the deuteration of hydride radicals, as their fundamental rotational transitions are at high frequencies where the atmosphere is mostly opaque. Nitrogen hydride radicals are important species i…
The 15N isotopologue abundance ratio measured today in different bodies of the solar system is thought to be connected to 15N-fractionation effects that would have occured in the protosolar nebula. The present study aims at putting constraints on the degree of 15N-fractionation that occurs during the prestellar phase, through observations of D, 13C and 15N-substituted isotopologues towards B1b. Both molecules from the nitrogen hydride family, i.e. N2H+ and NH3, and from the nitrile family, i.e. HCN, HNC and CN, are considered in the analysis. As a first step, we model the continuum emission in…
High nitrogen and carbon isotopic ratios in the interstellar comet 3I/ATLAS
University of Edinburgh（爱丁堡大学）；University of Liège（列日大学）；United States Naval Academy（美国海军学院）；Northumbria University（诺森比亚大学）；Auburn University（奥本大学）；Pontificia Universidad Católica de Chile（智利天主教 Pontificia 大学）；Catholic University of America（美利坚天主教大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；University of Helsinki（赫尔辛基大学）；University of Padova（帕多瓦大学）
The isotopic ratio of nitrogen presents a wide range of values in the Solar System and in star forming system whose origin is still unclear. Chemical reactions in the gas phase are one of the possible processes that could modify the $^{14}$N/$^{15}$N ratio. We aim at investigating if and how the passage of a shock wave in the interstellar medium, can affect the relative fraction of nitrogen isotopes. The ideal place for such a study is the L1157 outflow, where several shocked clumps are present. We present the first measurement of the $^{14}$N/$^{15}$N ratio in the two shocked clumps, B1 and B…
The isotopic ratio of nitrogen in nearby protoplanetary disks, recently measured in CN and HCN, indicates that a fractionated reservoir of nitrogen is available at the stage of comet formation. This reservoir presents a 3:1 enrichment in 15N relative to the elemental ratio of 330, identical to that between comets and the sun, suggesting that similar processes are responsible for the fractionation in the protosolar nebula (PSN) and in PSN analogs. However, how the fractionation of nitrogen takes place is an open question. Previously obtained HCN/HC15N abundance ratios suggest that HCN may be en…
Isotopic ratios of heavy elements are a key signature of the nucleosynthesis processes in stellar interiors. The contribution of successive generations of stars to the metal enrichment of the Universe is imprinted on the evolution of isotopic ratios over time. We investigate the isotopic ratios of carbon, nitrogen, oxygen, and sulfur through millimeter molecular absorption lines arising in the z=0.68 absorber toward the blazar B 0218+357. We find that these ratios differ from those observed in the Galactic interstellar medium, but are remarkably close to those in the only other source at inter…
Context: The depletion of heavy elements in cold cores of interstellar molecular clouds can lead to a situation where deuterated forms of H_3^+ are the most useful spectroscopic probes of the physical conditions. Aims: The aim is to predict the observability of the rotational lines of H_2D^+ and D_2H^+ from prestellar cores. Methods: Recently derived rate coefficients for the H_3^+ + H_2 isotopic system were applied to the "complete depletion" reaction scheme to calculate abundance profiles in hydrostatic core models. The ground-state lines of H_2D^+(o) (372 GHz) and D_2H^+(p) (692 GHz) arisin…
Context: The $^{15}$N fractionation has been observed to show large variations among astrophysical sources, depending both on the type of target and on the molecular tracer used. These variations cannot be reproduced by the current chemical models. Aims: Until now, the $^{14}$N/$^{15}$N ratio in N$_2$H$^+$ has been accurately measured in only one prestellar source, L1544, where strong levels of fractionation, with depletion in $^{15}$N, are found ($^{14}$N/$^{15}$N$\: \approx 1000$). In this paper we extend the sample to three more bona fide prestellar cores, in order to understand if the anti…
Nitrogen isotopic ratios are a key tool for tracing Galactic stellar nucleosynthesis. We present the first study of the $^{14}$N/$^{15}$N abundance ratio in the outer regions of the Milky Way (namely, for galactocentric distances, $R_{\rm GC}$, from 12 kpc up to 19 kpc), with the aim to study the stellar nucleosynthesis effects in the global Galactic trend. We analysed IRAM 30m observations towards a sample of 35 sources in the context of the CHEMical complexity in star-forming regions of the OUTer Galaxy (CHEMOUT) project. We derived the $^{14}$N/$^{15}$N ratios from HCN and HNC for 14 and 3 …
We present an IRAM 30m line survey of the dense core L483 in the 3 mm band. We detected 71 molecules (140 including different isotopologs), most of which are present in the cold and quiescent ambient cloud. Of particular interest among the detected molecules are the cis isomer of HCOOH, the complex organic molecules HCOOCH3, CH3OCH3, and C2H5OH, a wide variety of carbon chains, nitrogen oxides like N2O, and saturated molecules like CH3SH. In general, fractional molecular abundances in L483 are systematically lower than in TMC-1 (especially for carbon chains), tend to be higher than in L1544 an…
In star forming regions in our own Galaxy, the 14N/15N ratio is found to vary from $\sim$ 100 in meteorites, comets and protoplanetary disks up to $\sim$ 1000 in pre-stellar and star forming cores, while in external galaxies the very few single-dish large scale measurements of this ratio lead to values of 100-450. The extent of the contribution of isotopic fractionation to these variations is, to date, unknown. In this paper we present a theoretical chemical study of nitrogen fractionation in external galaxies in order to determine the physical conditions that may lead to a spread of the 14N/1…
Isotopic ratios provide a powerful tool for understanding the origins of materials, including the volatile and refractory matter within solar system bodies. Recent high sensitivity observations of molecular isotopologues, in particular with ALMA, have brought us new information on isotopic ratios of hydrogen, carbon, nitrogen and oxygen in star and planet forming regions as well as the solar system objects. Solar system exploration missions, such as Rosetta and Cassini, have given us further new insights. Meanwhile, the recent development of sophisticated models for isotope chemistry including…
We performed sensitive observations of the N15ND+(1-0) and 15NND+(1-0) lines toward the prestellar core L1544 using the IRAM 30m telescope. The lines are not detected down to 3 sigma levels in 0.2 km/s channels of around 6 mK. The non-detection provides the lower limit of the 14N/15N ratio for N2D+ of ~700-800, which is much higher than the elemental abundance ratio in the local ISM of ~200-300. The result indicates that N2 is depleted in 15N in the central part of L1544, because N2D+ preferentially traces the cold dense gas, and because it is a daughter molecule of N2. In-situ chemistry is un…
Understanding the processes that could lead to enrichment of molecules in $^{15}$N atoms is of particular interest in order to shed light on the relatively large variations observed in the $^{14}$N/$^{15}$N ratio in various solar system environments. Currently, the sample of molecular clouds where $^{14}$N/$^{15}$N ratios have been measured is small and has to be enlarged in order to allow statistically significant studies. In particular, the N$_2$H$^+$ molecule currently shows the largest spread of $^{14}$N/$^{15}$N ratios in high-mass star forming regions. However, the $^{14}$N/$^{15}$N rati…
Abundances of light elements in dwarf stars of different ages are important constraints for stellar yields, Galactic chemical evolution and exoplanet chemical composition studies. We have measured C and N abundances and $^{12}$C/$^{13}$C ratios for a sample of 63 solar twins spanning a wide range in age, based on spectral synthesis of a comprehensive list of CH\,A-X and CN\,B-X features using HARPS spectra. The analysis of 55 thin disc solar twins confirms the dependences of [C/Fe] and [N/Fe] on [Fe/H]. [N/Fe] is investigated as a function of [Fe/H] and age for the first time for these stars. …
Isotopic fractionation is an important tool to investigate the chemical history of our Solar System (SS). In particular, the isotopic fraction of nitrogen (14N/15N) is lower in comets and other pristine SS bodies with respect to the value measured for the protosolar nebula, suggesting a local chemical enrichment of 15N during the SS formation. Therefore, interferometric studies of nitrogen fractionation in SS precursors are imperative for us to obtain clues about our astrochemical origins. In this work, we investigated the variation of the 14N/15N ratio in one of the closest analogues of the e…
Ammonia is one of the best tracers of cold dense cores. It is also a minor constituent of interstellar ices and, as such, one of the important nitrogen reservoirs in the protosolar nebula, together with the gas phase nitrogen, in the form of N2 and N. An important diagnostic of the various nitrogen sources and reservoirs of nitrogen in the Solar System is the 14N/15N isotopic ratio. While good data exist for the Solar System, corresponding measurements in the interstellar medium are scarce and of low quality. Following the successful detection of the singly, doubly, and triply deuterated isoto…
The nitrogen chemical evolution during star and planet formation is still not fully understood. Ammonia (NH$_3$) is a key specie in the understanding of the molecular evolution in star-forming clouds and nitrogen isotope fractionation. In this paper, we present high spatial resolution observations of multiple emission lines of NH$_3$ toward the protobinary system NGC1333 IRAS4A with Karl G. Jansky Very Large Array (VLA). We spatially resolved the binary (hereafter 4A1 and 4A2) and detected compact emission of NH$_3$ transitions with high excitation energies ($\gtrsim$100 K) from the vicinity o…
We present VLA NH3 and PdBI NH2D and H13NC observations of the star forming core ahead of HH 80N, the optically obscured northern counterpart of the Herbig-Haro objects HH 80/81. The main goal is to determine the kinematical information of the high density regions of the core ($n\lesssim 10^5$ cm$^{-3}$), missed in previous works due to the depletion of the species observed (e.g. CS). The obtained maps show different kinematical signatures between the eastern and western parts of the core, suggesting a possible dynamical interaction of the core with the HH 80/81/80N outflow. The analysis of th…
We show the first interferometric maps of the 14N/15N ratio obtained with the Atacama Large Millimeter Array (ALMA) towards the Solar-like forming protocluster OMC-2 FIR4. We observed N2H+, 15NNH+, N15NH+ (1-0), and N2D+ (2-1), from which we derive the isotopic ratios 14N/15N and D/H. The target is one of the closest analogues of the environment in which our Sun may have formed. The ALMA images, having synthesised beam corresponding to ~600 au, show that the emission of the less abundant isotopologues is distributed in several cores of ~10" (i.e. ~0.02~pc or 4000 au) embedded in a more extende…
Nitrogen is one of the most abundant elements in the Universe and its 14N/15N isotopic ratio has the potential to provide information about the initial environment in which our Sun formed. Recent findings suggest that the Solar System may have formed in a massive cluster since the presence of short-lived radioisotopes in meteorites can only be explained by the influence of a supernova. The aim of this project is to determine the 14N/15N ratio towards a sample of cold, massive dense cores at the initial stages in their evolution. We have observed the J=1-0 transitions of HCN, H13CN, HC15N, HN13…
We investigated the chemistry of nitrogen--containing species, principally isotopomers of CN, HCN, and HNC, in a sample of pre-protostellar cores. We used the IRAM 30 m telescope to measure the emission in rotational and hyperfine transitions of CN, HCN, 13CN, H13CN, HN13C, and HC15N, in L 1544, L 183, Oph D, L 1517B, L 310. The observations were made along axial cuts through the dust emission peak, at a number of regularly--spaced offset positions. The observations were reduced and analyzed to obtain the column densities, using the measurements of the less abundant isotopic variants in order …
(Abridged) The terrestrial planets, comets, and meteorites are significantly enriched in 15N compared to the Sun and Jupiter. While the solar and jovian nitrogen isotope ratio is believed to represent the composition of the protosolar nebula, a still unidentified process has caused 15N-enrichment in the solids. Several mechanisms have been proposed to explain the variations, including chemical fractionation. However, observational results that constrain the fractionation models are scarce. While there is evidence of 15N-enrichment in prestellar cores, it is unclear how the signature evolves in…
The ratio between the two stable isotopes of nitrogen, $^{14}$N and $^{15}$N, is well measured in the terrestrial atmosphere ($\sim 272$), and in the pre-Solar nebula ($\sim 441$). Interestingly, some pristine Solar System materials show enrichments in $^{15}$N with respect to the pre-Solar nebula value. However, it is not yet clear if, and how, these enrichments are linked to the past chemical history, due to the limited number of measurements in dense star-forming regions. In this respect, dense cores believed to be precursors of clusters containing also intermediate- and high-mass stars are…
A tale of two isotopes: Spatial variation in HCN fractionation toward young cores
Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；Centro de Astrobiología (CAB), CSIC-INTA（天体生物学中心（CAB），西班牙国家科学研究委员会-国家航空技术研究所）；European Southern Observatory（欧洲南方天文台）
