Modeling deuterium chemistry in starless cores: full scrambling versus proton hop

Sipilä, O.; Caselli, P.; Harju, J.

doi:10.1051/0004-6361/201936416

Cited by 30 publications

(19 citation statements)

References 30 publications

(55 reference statements)

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“…The high deuterium fractionation of our sample might then result from the accumulation of [NH 2 D]/[NH 3 ] ratios of individual clumps within the beam. NH 3 deuteration as high as our observed values is obtained by the model of Sipilä et al (2019), which limits proton-donation reactions to proceed only through proton hop (cf. Hily-Blant et al 2018).…”

Section: Comparison Of Nh 3 Deuteration In Atlasgal Sources With Other Samplessupporting

confidence: 62%

“…These [NH 2 D]/[NH 3 ] ratios are consistent with those of the ATLASGAL sources, although we estimate an even higher deuteration than Pillai et al (2007), up to 1.6 in a few ATLASGAL clumps. Recently, Sipilä et al (2019) compared two approaches to model deuterium fractionation that differ in their mechanism to describe ion-molecule proton-donation reactions. The full scrambling model comprises multiple interchanges of atoms including for example proton hop and proton exchange (Oka 2004).…”

Section: Comparison Of Nh 3 Deuteration In Atlasgal Sources With Other Samplesmentioning

confidence: 99%

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ATLASGAL-selected massive clumps in the inner Galaxy

Wienen

Wyrowski

Walmsley

et al. 2021

A&A

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Context. Deuteration has been used as a tracer of the evolutionary phases of low- and high-mass star formation. The APEX Telescope Large Area Survey (ATLASGAL) provides an important repository for a detailed statistical study of massive star-forming clumps in the inner Galactic disc at different evolutionary phases. Aims. We study the amount of deuteration using NH2D in a representative sample of high-mass clumps discovered by the ATLASGAL survey covering various evolutionary phases of massive star formation. The deuterium fraction of NH3 is derived from the NH2D 111−101 ortho transition at ~86 GHz and NH2D 111−101 para line at ~110 GHz. This is refined for the first time by measuring the NH2D excitation temperature directly with the NH2D 212–202 para transition at ~74 GHz. Any variation of NH3 deuteration and ortho-to-para ratio with the evolutionary sequence is analysed. Methods. Unbiased spectral line surveys at 3 mm were conducted towards ATLASGAL clumps between 85 and 93 GHz with the Mopra telescope and from 84 to 115 GHz using the IRAM 30m telescope. A subsample was followed up in the NH2D transition at 74 GHz with the IRAM 30m telescope. We determined the deuterium fractionation from the column density ratio of NH2D and NH3 and measured the NH2D excitation temperature for the first time from the simultaneous modelling of the 74 and 110 GHz line using MCWeeds. We searched for trends in NH3 deuteration with the evolutionary sequence of massive star formation. We derived the column density ratio from the 86 and 110 GHz transitions as an estimate of the NH2D ortho-to-para ratio. Results. We find a large range of the NH2D to NH3 column density ratio up to 1.6 ± 0.7 indicating a high degree of NH3 deuteration in a subsample of the clumps. Our analysis yields a clear difference between NH3 and NH2D rotational temperatures for a fraction. We therefore advocate observation of the NH2D transitions at 74 and 110 GHz simultaneously to determine the NH2D temperature directly. We determine a median ortho-to-para column density ratio of 3.7 ± 1.2. Conclusions. The high detection rate of NH2D confirms a high deuteration previously found in massive star-forming clumps. Using the excitation temperature of NH2D instead of NH3 is needed to avoid an overestimation of deuteration. We measure a higher detection rate of NH2D in sources at early evolutionary stages. The deuterium fractionation shows no correlation with evolutionary tracers such as the NH3 (1,1) line width, or rotational temperature.

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Section: Comparison Of Nh 3 Deuteration In Atlasgal Sources With Other Samplessupporting

confidence: 62%

Section: Comparison Of Nh 3 Deuteration In Atlasgal Sources With Other Samplesmentioning

confidence: 99%

ATLASGAL-selected massive clumps in the inner Galaxy

Wienen

Wyrowski

Walmsley

et al. 2021

A&A

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“…For the chemical simulations we use our gas-grain chemical code, recently described in Sipilä et al (2019aSipilä et al ( , 2019b. The chemical networks used here contain deuterium and spin-state chemistry (see Sipilä et al 2019b, and references therein).…”

Section: Description Of the Modelsmentioning

confidence: 99%

First survey of HCNH$^+$ in high-mass star-forming cloud cores

Fontani,

Colzi,

Redaelli

et al. 2021

Preprint

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Context. Most stars in the Galaxy, including the Sun, were born in high-mass star-forming regions. It is hence important to study the chemical processes in these regions to better understand the chemical heritage of both the Solar System and most stellar systems in the Galaxy. Aims. The molecular ion HCNH + is thought to be a crucial species in ion-neutral astrochemical reactions, but so far it has been detected only in a handful of star-forming regions, and hence its chemistry is poorly known. Methods. We have observed with the IRAM-30m Telescope 26 high-mass star-forming cores in different evolutionary stages in the J = 3 − 2 rotational transition of HCNH + . Results. We report the detection of HCNH + in 16 out of 26 targets. This represents the largest sample of sources detected in this molecular ion so far. The fractional abundances of HCNH + with respect to H 2 , [HCNH + ], are in the range 0.9 − 14 × 10 −11 , and the highest values are found towards cold starless cores, for which [HCNH + ] is of the order of 10 −10 . The abundance ratios [HCNH + ]/[HCN] and [HCNH + ]/[HCO + ] are both ≤ 0.01 for all objects except for four starless cores, for which they are well above this threshold. These sources have the lowest gas temperature and average H 2 volume density in the sample. Based on this observational difference, we run two chemical models, a "cold" one and a "warm" one, which attempt to match as much as possible the average physical properties of the cold(er) starless cores and of the warm(er) targets. The reactions occurring in the latter case are investigated in this work for the first time. Our predictions indicate that in the warm model HCNH + is mainly produced by reactions with HCN and HCO + , while in the cold one the main progenitor species of HCNH + are HCN + and HNC + . Conclusions. The observational results indicate, and the model predictions confirm, that the chemistry of HCNH + is different in cold/early and warm/evolved cores, and the abundance ratios [HCNH + ]/[HCN] and [HCNH + ]/[HCO + ] can be a useful astrochemical tool to discriminate between different evolutionary phases in the process of star formation.

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“…Increasing attention is being paid to the accurate modeling of the deuterium chemistry as a tool to probe the evolution of the dense gas during the starless core phase (see, e.g., Sipilä et al 2010Sipilä et al , 2015Roueff et al 2015;Majumdar et al 2017). One key aspect is the realization of the importance of the spin state in deuterium chemistry (Sipilä et al 2019), since multiply-hydrogenated or deuterated molecules can exist in several forms due to the different nuclear spin states. Majumdar et al (2017) presented the first publicly available chemical network for Nautilus (Ruaud et al 2016) with deuterated species and spin chemistry in its two-phase implementation where the gas phase and grain phase interact.…”

Section: Introductionmentioning

confidence: 99%

Evolutionary view through the starless cores in Taurus: deuteration in TMC 1-C and TMC 1-CP

Navarro-Almaida,

Fuente,

Majumdar

et al. 2021

Preprint

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Context. The chemical and physical evolution of starless and pre-stellar cores are of paramount importance to understanding the process of star formation. The Taurus Molecular Cloud cores TMC 1-C and TMC 1-CP share similar initial conditions and provide an excellent opportunity to understand the evolution of the pre-stellar core phase. Aims. We investigated the evolutionary stage of starless cores based on observations towards the prototypical dark cores TMC 1-C and TMC 1-CP. Methods. We mapped the prototypical dark cores TMC 1-C and TMC 1-CP in the CS 3 → 2,→ 0, and N2D + 1 → 0 transitions. We performed a multi-transitional study of CS and its isotopologs, DCN, and DNC lines to characterize the physical and chemical properties of these cores. We studied their chemistry using the state-of-the-art gas-grain chemical code Nautilus and pseudo time-dependent models to determine their evolutionary stage. Results. The central nH volume density, the N2H + column density, and the abundances of deuterated species are higher in TMC 1-C than in TMC 1-CP, yielding a higher N2H + deuterium fraction in TMC 1-C, thus indicating a later evolutionary stage for TMC 1-C. The chemical modeling with pseudo time-dependent models and their radiative transfer are in agreement with this statement, allowing us to estimate a collapse timescale of ∼ 1 Myr for TMC 1-C. Models with a younger collapse scenario or a collapse slowed down by a magnetic support are found to more closely reproduce the observations towards TMC 1-CP. Conclusions. Observational diagnostics seem to indicate that TMC 1-C is in a later evolutionary stage than TMC 1-CP, with a chemical age ∼1 Myr. TMC 1-C shows signs of being an evolved core at the onset of star formation, while TMC 1-CP appears to be in an earlier evolutionary stage due to a more recent formation or, alternatively, a collapse slowed down by a magnetic support.

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Modeling deuterium chemistry in starless cores: full scrambling versus proton hop

Cited by 30 publications

References 30 publications

ATLASGAL-selected massive clumps in the inner Galaxy

ATLASGAL-selected massive clumps in the inner Galaxy

First survey of HCNH$^+$ in high-mass star-forming cloud cores

Evolutionary view through the starless cores in Taurus: deuteration in TMC 1-C and TMC 1-CP

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