Nitrogen isotope fractionation in protoplanetary disks

Visser, R.; Bruderer, S.; Cazzoletti, P.; Facchini, Stefano; Heays, A. N.; Dishoeck, E. F. van

doi:10.1051/0004-6361/201731898

Cited by 81 publications

(125 citation statements)

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“…At higher density, all lines are thermalized (models at n H 2 higher than 10 9 cm −3 are not shown). From the generic chemical models of Visser et al (2018), it appears that HCN is concentrated at radii r = 5 − 50 au and scale heights z/r = 0.2 to 0.3, where the gas kinetic temperature is ≈ 200K and the density in the range 10 6 to 10 8 cm −3 , which would indicate that the single excitation temperature assumption fails. On the other hand, the FWHM of the HCN, H 13 CN, and HC 15 N lines at a radius of 0.6 (≈35 au) and beyond is ≈ 0.35 km s −1 (see Table B.3), placing a conservative upper limit on the kinetic temperature of (Teague et al 2016)…”

Section: Discussionmentioning

confidence: 99%

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Hily-Blant

Souza

Kastner

et al. 2019

A&A

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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 14 N/ 15 N isotopic ratio. Disks that orbit pre-main-sequence (TTauri) stars provide unique opportunities for observing the chemical content of analogs of the protosolar nebula and therefore for building a comprehensive scenario that can explain the origin of nitrogen in the Solar System and in planetforming disks. With ALMA, it has become possible to measure isotopic ratios of nitrogen-bearing species in such environments. We present spectrally and spatially resolved observations of the hyperfine structure of the 4-3 rotational transition of HCN and its main isotopologs H 13 CN and HC 15 N in the disk orbiting the 8 Myr old TTauri star TW Hya. The sensitivity allows directly measuring the HCN/H 13 CN and HCN/HC 15 N abundance ratios with minimal assumptions. Averaged spatially over the disks, the ratios are 86±4 and 223±21, respectively. The latter value is significantly lower than the CN/C 15 N ratio of 323±30 in this disk and thus provides the first evidence that two isotopic reservoirs of nitrogen are present in a disk at the stage of giant planet and comet formation. Furthermore, we find clear evidence for an increase in the ratio of HCN to HC 15 N with radius. The ratio in the outer disk, at 45 au, is 339±28, in excellent agreement with direct measurements in the local interstellar medium, and with the bulk nitrogen isotopic ratio predicted from galactic evolution calculations. In the comet formation region at r = 20 au, the ratio is a factor ≈ 3 lower, 121±11. This radial increase qualitatively agrees with the scenario in which selective photodissociation of N 2 is the dominant fractionation process. However, our isotopic ratios and kinetic temperature of the HCN-emitting layers quantitatively disagree with models of nitrogen chemistry in disks.

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Section: Discussionmentioning

confidence: 99%

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Hily-Blant

Souza

Kastner

et al. 2019

A&A

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“…High temperatures and densities of the shocked gas are responsible for HCN production. The enhancement of the HCN emission in shocks arises due to the H 2 + CN → HCN + H reaction (Bruderer et al 2009;Visser et al 2018), which has an activation barrier of 960 K (Baulch et al 2005). Both models and observations suggest orders of magnitude increase in HCN abundance for gas temperatures above 200 K (Boonman et al 2001;Lahuis et al 2007).…”

Section: Hcnmentioning

confidence: 99%

Chemical and kinematic structure of extremely high-velocity molecular jets in the Serpens Main star-forming region

Tychoniec

Hull

Kristensen

et al. 2019

A&A

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Context. Outflows are one of the first signposts of ongoing star formation. The fastest molecular component to the protostellar outflows -extremely high-velocity (EHV) molecular jets -are still puzzling since they are seen only rarely. As they originate deep inside the embedded protostar-disk system, they provide vital information about the outflow-launching process in the earliest stages. Aims. The first aim is to analyze the interaction between the EHV jet and the slow outflow by comparing their outflow force content. The second aim is to analyze the chemical composition of the different outflow velocity components and to reveal the spatial location of molecules. Methods. ALMA 3 mm (Band 3) and 1.3 mm (Band 6) observations of five outflow sources at 0 . 3 -0 . 6 (130 -260 au) resolution in the Serpens Main cloud are presented. Observations of CO, SiO, H 2 CO and HCN reveal the kinematic and chemical structure of those flows. Three velocity components are distinguished: the slow and the fast wing, and the EHV jet. Results. Out of five sources, three have the EHV component. Comparison of outflow forces reveals that only the EHV jet in the youngest source Ser-emb 8 (N) has enough momentum to power the slow outflow. The SiO abundance is generally enhanced with velocity, while HCN is present in the slow and the fast wing, but disappears in the EHV jet. For Ser-emb 8 (N), HCN and SiO show a bow-shock shaped structure surrounding one of the EHV peaks suggesting sideways ejection creating secondary shocks upon interaction with the surroundings. Also, the SiO abundance in the EHV gas decreases with distance from this protostar, whereas that in the fast wing increases. H 2 CO is mostly associated with low-velocity gas but also appears surprisingly in one of the bullets in the Ser-emb 8 (N) EHV jet. No complex organic molecules are found to be associated with the outflows. Conclusions. The high detection rate suggests that the presence of the EHV jet may be more common than previously expected. The EHV jet alone does not contain enough outflow force to explain the entirety of the outflowing gas. The origin and temporal evolution of the abundances of SiO, HCN and H 2 CO through high-temperature chemistry are discussed. The data are consistent with a low C/O ratio in the EHV gas versus high C/O ratio in the fast and slow wings.

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“…Charnley & Rodgers (2002) theorized that reactions of 15 N-enriched N 2 with He + , followed by H 2 , can lead to the production of 15 N-enriched interstellar NH 3 ice. In the protosolar nebula, 15 N-enriched NH 3 may have also arisen following the isotope-selective photodissociation of N 2 (Visser et al 2018). Understanding Titan's atmospheric 14 N/ 15 N ratio may thus provide a crucial window into the thermal, chemical, and radiation history of its nitrogen-bearing ices.…”

Section: Introductionmentioning

confidence: 99%

Interferometric Imaging of Titan’s HC₃N, H¹³CCCN, and HCCC¹⁵N

Cordiner

Nixon

Charnley

et al. 2018

ApJL

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We present the first maps of cyanoacetylene isotopologues in Titan's atmosphere, including H 13 CCCN and HCCC 15 N, detected in the 0.9mm band using the Atacama Large Millimeter/submillimeter array (ALMA) around the time of Titan's (southern winter) solstice in 2017 May. The first high-resolution map of HC 3 N in its v 7 = 1 vibrationally excited state is also presented, revealing a unique snapshot of the global HC 3 N distribution, free from the strong optical depth effects that adversely impact the ground-state (v = 0) map. The HC 3 N emission is found to be strongly enhanced over Titan's south pole (by a factor of 5.7 compared to the north pole), consistent with rapid photochemical loss of HC 3 N from the summer hemisphere combined with production and transport to the winter pole since the 2015 April ALMA observations. The H 13 CCCN/HCCC 15 N flux ratio is derived at the southern HC 3 N peak, and implies an HC 3 N/HCCC 15 N ratio of 67 ± 14. This represents a significant enrichment in 15 N compared with Titan's main molecular nitrogen reservoir, which has a 14 N/ 15 N ratio of 167, and confirms the importance of photochemistry in determining the nitrogen isotopic ratio in Titan's organic inventory.

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Nitrogen isotope fractionation in protoplanetary disks

Cited by 81 publications

References 83 publications

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Chemical and kinematic structure of extremely high-velocity molecular jets in the Serpens Main star-forming region

Interferometric Imaging of Titan’s HC₃N, H¹³CCCN, and HCCC¹⁵N

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Nitrogen isotope fractionation in protoplanetary disks

Cited by 81 publications

References 83 publications

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Multiple nitrogen reservoirs in a protoplanetary disk at the epoch of comet and giant planet formation

Chemical and kinematic structure of extremely high-velocity molecular jets in the Serpens Main star-forming region

Interferometric Imaging of Titan’s HC3N, H13CCCN, and HCCC15N

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Interferometric Imaging of Titan’s HC₃N, H¹³CCCN, and HCCC¹⁵N