Fine and hyperfine excitation of C2H by collisions with He at low temperature

Spielfiedel, A.; Feautrier, N.; Najar, Faouzi; Abdallah, D. Ben; Dayou, Fabrice; Senent, María Luisa; Lique, François

doi:10.1111/j.1365-2966.2011.20225.x

Cited by 52 publications

(39 citation statements)

References 44 publications

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“…Thus we have to extrapolate the rate coefficients from Spielfiedel et al (2012) in terms of both additional levels and higher temperatures. A very general, but numerically demanding approach to extrapolating collision rates was proposed by Neufeld (2010).…”

Section: Discussionmentioning

confidence: 99%

“…The recent access to the higher rotational transitions provided by the Herschel Space Observatory and the recently calculated inelastic collision rates (Spielfiedel et al 2012) give an opportunity to probe the chemistry and excitation of C 2 H. Using the higher rotational transitions accessible by Herschel and the available collision rates we probe the excitation of C 2 H and the physical parameters that it traces toward the prototypical, high UV-illumination PDR, the Orion Bar. As photodissociation of larger carbon-chain molecules and polycyclic aromatic hydrocarbons (PAHs) is one of the possible formation routes of C 2 H, PDRs provide a good source to study C 2 H. A&A 578, A124 (2015) of the Orion Bar is equivalent to (1−4) × 10 4 χ 0 in Draine (1978) units.…”

Section: Introductionmentioning

confidence: 99%

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C₂H observations toward the Orion Bar

Nagy

Ossenkopf

Tak

et al. 2015

A&A

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Context. The ethynyl radical (C 2 H) is one of the first radicals to be detected in the interstellar medium. Its higher rotational transitions have recently become available with the Herschel Space Observatory. Aims. We aim to constrain the physical parameters of the C 2 H emitting gas toward the Orion Bar. Methods. We analyze the C 2 H line intensities measured toward the Orion Bar CO + Peak and Herschel/HIFI maps of C 2 H, CH, and HCO + and a NANTEN map of [Ci]. We interpret the observed C 2 H emission using the combination of Herschel/HIFI and NANTEN data with radiative transfer and PDR models. Results. Five rotational transitions of C 2 H (from N = 6−5 up to N = 10−9) have been detected in the HIFI frequency range toward the CO + peak of the Orion Bar. Based on the five detected C 2 H transitions, a single component rotational diagram analysis gives a rotation temperature of ∼64 K and a beam-averaged C 2 H column density of 4 × 10 13 cm −2 . The rotational diagram is also consistent with a two-component fit, resulting in rotation temperatures of 43 ± 0.2 K and 123 ± 21 K and in beam-averaged column densities of ∼8.3 × 10 13 cm −2 and ∼2.3 × 10 13 cm −2 for the three lower-N and for the three higher-N transitions, respectively. The measured five rotational transitions cannot be explained by any single parameter model. According to a non-LTE model, most of the C 2 H column density produces the lower−N C 2 H transitions and traces a warm (T kin ∼ 100−150 K) and dense (n(H 2 ) ∼ 10 5 −10 6 cm −3 ) gas. A small fraction of the C 2 H column density is required to reproduce the intensity of the highest-N transitions (N = 9−8 and N = 10−9) originating in a high-density (n(H 2 ) ∼ 5×10 6 cm −3 ) hot (T kin ∼ 400 K) gas. The total beam-averaged C 2 H column density in the model is 10 14 cm −2 . A comparison of the spatial distribution of C 2 H to those of CH, HCO + , and [Ci] shows the best correlation with CH. Conclusions. Both the non-LTE radiative transfer model and a simple PDR model representing the Orion Bar with a planeparallel slab of gas and dust suggest that C 2 H cannot be described by a single pressure component, unlike the reactive ion CH + , which was previously analyzed toward the Orion Bar CO + peak. The physical parameters traced by the higher rotational transitions (N = 6−5, ..., 10−9) of C 2 H may be consistent with the edges of dense clumps exposed to UV radiation near the ionization front of the Orion Bar.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

C₂H observations toward the Orion Bar

Nagy

Ossenkopf

Tak

et al. 2015

A&A

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“…We have therefore re-analyzed the excitation characteristics of this emission using RADEX (van der Tak et al 2007) and the state to state collision rates by Spielfiedel et al (2012). This analysis is shown in Figure 12.…”

Section: ( )mentioning

confidence: 99%

Hydrocarbon Emission Rings in Protoplanetary Disks Induced by Dust Evolution

Bergin

Cleeves

et al. 2016

ApJ

211

278

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We report observations of resolved C 2 H emission rings within the gas-rich protoplanetary disks of TWHya and DMTau using the Atacama Large Millimeter Array. In each case the emission ring is found to arise at the edge of the observable disk of millimeter-sized grains (pebbles) traced by submillimeter-wave continuum emission. In addition, we detect a C 3 H 2 emission ring with an identical spatial distribution to C 2 H in the TWHya disk. This suggests that these are hydrocarbon rings (i.e., not limited to C 2 H). Using a detailed thermo-chemical model we show that reproducing the emission from C 2 H requires a strong UV field and C/O>1 in the upper disk atmosphere and outer disk, beyond the edge of the pebble disk. This naturally arises in a disk where the ice-coated dust mass is spatially stratified due to the combined effects of coagulation, gravitational settling and drift. This stratification causes the disk surface and outer disk to have a greater permeability to UV photons. Furthermore the concentration of ices that transport key volatile carriers of oxygen and carbon in the midplane, along with photochemical erosion of CO, leads to an elemental C/O ratio that exceeds unity in the UV-dominated disk. Thus the motions of the grains, and not the gas, lead to a rich hydrocarbon chemistry in disk surface layers and in the outer disk midplane.

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“…(d) Far distance; the distance ambiguity of the IRAS source was resolved by Sewilo et al (2004). Reitblat (1980); Padovani et al (2009);Spielfiedel et al (2012). (k) n crit at 20 K. (l) Lapinov et al (2007).…”

Section: Spectra and Line Parametersmentioning

confidence: 99%

A MALT90 study of the chemical properties of massive clumps and filaments of infrared dark clouds

Miettinen

2014

A&A

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Context. Infrared dark clouds (IRDCs) provide a useful testbed in which to investigate the genuine initial conditions and early stages of massive-star formation. Aims. We attempt to characterise the chemical properties of a sample of 35 massive clumps of IRDCs through multi-molecular line observations. We also search for possible evolutionary trends among the derived chemical parameters.Methods. The clumps are studied using the MALT90 (Millimetre Astronomy Legacy Team 90 GHz) line survey data obtained with the Mopra 22 m telescope. The survey covers 16 different transitions near 90 GHz. The spectral-line data are used in concert with our previous LABOCA (Large APEX BOlometer CAmera) 870 μm dust emission data. Results. Eleven MALT90 transitions are detected towards the clumps at least at the 3σ level. Most of the detected species (SiO, C 2 H, HNCO, HCN, HCO + , HNC, HC 3 N, and N 2 H + ) show spatially extended emission towards many of the sources. Most of the fractional abundances of the molecules with respect to H 2 are found to be comparable to those determined in other recent similar studies of IRDC clumps. We found that the abundances of SiO, HNCO, and HCO + are higher in IR-bright clumps than in IR-dark sources, reflecting a possible evolutionary trend. A hint of this trend is also seen for HNC and HC 3 N. An opposite trend is seen for the C 2 H and N 2 H + abundances. Moreover, a positive correlation is found between the abundances of HCO + and HNC, and between those of HNC and HCN. The HCN and HNC abundances also appear to increase as a function of the N 2 H + abundance. The HNC/HCN and N 2 H + /HNC abundance ratios are derived to be near unity on average, while that of HC 3 N/HCN is ∼10%. The N 2 H + /HNC ratio appears to increase as the clump evolves, while the HNC/HCO + ratio shows the opposite behaviour. Conclusions. The detected SiO emission is probably caused by shocks driven by outflows in most cases, although shocks resulting from the cloud formation process could also play a role. Shock-origin for the HNCO, HC 3 N, and CH 3 CN emission is also plausible. The average HNC/HCN ratio is in good agreement with those seen in other IRDCs, but gas temperature measurements would be neeeded to study its temperature dependence. Our results support the finding that C 2 H can trace the cold gas, and not just the photodissociation regions. The HC 3 N/HCN ratio appears to be comparable to the values seen in other types of objects, such as T Tauri disks and comets.

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Fine and hyperfine excitation of C2H by collisions with He at low temperature

Cited by 52 publications

References 44 publications

C₂H observations toward the Orion Bar

C₂H observations toward the Orion Bar

Hydrocarbon Emission Rings in Protoplanetary Disks Induced by Dust Evolution

A MALT90 study of the chemical properties of massive clumps and filaments of infrared dark clouds

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Fine and hyperfine excitation of C2H by collisions with He at low temperature

Cited by 52 publications

References 44 publications

C2H observations toward the Orion Bar

C2H observations toward the Orion Bar

Hydrocarbon Emission Rings in Protoplanetary Disks Induced by Dust Evolution

A MALT90 study of the chemical properties of massive clumps and filaments of infrared dark clouds

Contact Info

Product

Resources

About

C₂H observations toward the Orion Bar

C₂H observations toward the Orion Bar