Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Fonfría, J. P.; Agúndez, M.; Cernicharo, J.; Richter, Matthew J.; Lacy, J. H.

doi:10.3847/1538-4357/aa9ee0

Cited by 20 publications

(14 citation statements)

References 48 publications

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“…These scenarios could be compatible with the complex structure composed of thin arcs found in the envelope of IRC+10216 (Mauron & Huggins 1999, 2000; Leão et al 2006; Cernicharo et al 2015; Decin et al 2015; Quintana-Lacaci et al 2016; Guélin et al 2018). These structures are predicted to appear naturally in envelopes surrounding single stars by Woitke (2006) and in binary systems by Mastrodemos & Morris (1999), and/or with the peculiar formation of molecules such as H 2 O, C 2 H 4 , C 4 H 2 , and carbon chains close to the star (Agúndez et al 2010, 2017; Fonfría et al 2017a,b).…”

Section: Discussionmentioning

confidence: 99%

The Maser-emitting Structure and Time Variability of the SiS Lines J = 14–13 and 15–14 in IRC+10216*

Fonfría

Fernández-López

Pardo

et al. 2018

ApJ

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We present new high angular resolution interferometer observations of the = 0 = 14 - 13 and 15 - 14 SiS lines towards IRC+10216, carried out with CARMA and ALMA. The maps, with angular resolutions of reveal (1) an extended, roughly uniform, and weak emission with a size of (2) a component elongated approximately along the East-West direction peaking at at both sides of the central star, and (3) two blue- and red-shifted compact components peaking around to the NW of the star. We have modeled the emission with a 3D radiation transfer code finding that the observations cannot be explained only by thermal emission. Several maser clumps and one arc-shaped maser feature arranged from 5 to 20 from the central star, in addition to a thin shell-like maser structure at ≃ 13 are required to explain the observations. This maser emitting set of structures accounts for 75% of the total emission while the other 25% is produced by thermally excited molecules. About 60% of the maser emission comes from the extended emission and the rest from the set of clumps and the arc. The analysis of a time monitoring of these and other SiS and SiS lines carried out with the IRAM 30 m telescope from 2015 to present suggests that the intensity of some spectral components of the maser emission strongly depends on the stellar pulsation while other components show a mild variability. This monitoring evidences a significant phase lag of ≃ 0.2 between the maser and NIR light-curves.

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Section: Discussionmentioning

confidence: 99%

The Maser-emitting Structure and Time Variability of the SiS Lines J = 14–13 and 15–14 in IRC+10216*

Fonfría

Fernández-López

Pardo

et al. 2018

ApJ

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“…It is well known that the polymerization of C 2 H 2 gives rise to polyacetylenic chains (Cernicharo 2004), whose formation mechanism has been recently mapped with the Atacama Large Millimeter/submillimeter Array in the outer regions of the C-star envelope IRC +10216 (Agúndez et al 2017). Furthermore, diacetylene (C 4 H 2 ) has been recently detected in this star through high spectral resolution MIR observations (Fonfría et al 2018). Acetylene is also believed to play a crucial role in the formation of benzene and PAH compounds (Frenklach & Feigelson 1989).…”

Section: Introductionmentioning

confidence: 95%

The Chemistry of Cosmic Dust Analogs from C, C₂, and C₂H₂ in C-rich Circumstellar Envelopes

Santoro

Martínez

Lauwaet

et al. 2020

ApJ

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Interstellar carbonaceous dust is mainly formed in the innermost regions of circumstellar envelopes around carbonrich asymptotic giant branch stars (AGBs). In these highly chemically stratified regions, atomic and diatomic carbon, along with acetylene, are the most abundant species after H 2 and CO. In a previous study, we addressed the chemistry of carbon (C and C 2 ) with H 2 showing that acetylene and aliphatic species form efficiently in the dust formation region of carbon-rich AGBs whereas aromatics do not. Still, acetylene is known to be a key ingredient in the formation of linear polyacetylenic chains, benzene, and polycyclic aromatic hydrocarbons (PAHs), as shown by previous experiments. However, these experiments have not considered the chemistry of carbon (C and C 2 ) with C 2 H 2 . In this work, by employing a sufficient amount of acetylene, we investigate its gas-phase interaction with atomic and diatomic carbon. We show that the chemistry involved produces linear polyacetylenic chains, benzene, and other PAHs, which are observed with high abundances in the early evolutionary phase of planetary nebulae. More importantly, we have found a nonnegligible amount of pure and hydrogenated carbon clusters as well as aromatics with aliphatic substitutions, both being a direct consequence of the addition of atomic carbon. The incorporation of alkyl substituents into aromatics can be rationalized by a mechanism involving hydrogen abstraction followed by methyl addition. All the species detected in the gas phase are incorporated into nanometricsized dust analogs, which consist of a complex mixture of sp, sp 2 , and sp 3 hydrocarbons with amorphous morphology.

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“…C 4 H 2 has recently been detected in the outflow of IRC+10216 with a column density of (2.4 ± 1.5) × 10 16 cm −2 (Fonfría et al 2018). From the analysis of Fonfría et al (2018), it is suggested that the photodissociation occurs closer to the central star, due to, for example, a clumpy outer envelope.…”

Section: Appendix E2: C-rich Outflowsmentioning

confidence: 99%

“…From the analysis of Fonfría et al (2018), it is suggested that the photodissociation occurs closer to the central star, due to, for example, a clumpy outer envelope. Our models withṀ = 10 −5 M yr −1 yield a column density close to the observed value for highly porous one-component outflows.…”

Section: Appendix E2: C-rich Outflowsmentioning

confidence: 99%

Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow

Sande

Sundqvist

Millar

et al. 2018

A&A

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Publisher rights © 2018 ESO. This work is made available online in accordance with the publisher's policies. Please refer to any applicable terms of use of the publisher. General rightsCopyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. ABSTRACTContext. In the inner regions of asymptotic giant branch (AGB) outflows, several molecules have been detected with abundances much higher than those predicted from thermodynamic equilibrium chemical models. The presence of the majority of these species can be explained by shock-induced non-equilibrium chemical models, where shocks caused by the pulsating star take the chemistry out of equilibrium in the inner region. Moreover, a non-uniform density structure has been detected in several AGB outflows. Both largescale structures, such as spirals and disks, and small-scale density inhomogeneities or clumps have been observed. These structures may also have a considerable impact on the circumstellar chemistry. A detailed parameter study on the quantitative effects of a non-homogeneous outflow has so far not been performed. Aims. We examine the effects of a non-uniform density distribution within an AGB outflow on its chemistry by considering a stochastic, clumpy density structure. Methods. We implement a porosity formalism for treating the increased leakage of light associated with radiation transport through a clumpy, porous medium. We then use this method to examine the effects from the altered UV radiation field penetration on the chemistry, accounting also for the increased reaction rates of two-body processes in the overdense clumps. The specific clumpiness is determined by three parameters: the characteristic length scale of the clumps at the stellar surface, the clump volume filling factor, and the inter-clump density contrast. In this paper, the clumps are assumed to have a spatially constant volume filling factor, which implies that they expand as they move outward in the wind.Results. We present a parameter study of the effect of clumping and porosity on the chemistry throughout the outflow. Both the higher density within the clumps and the increased UV radiation field penetration have an important impact on the chemistry, as they both alter the chemical pathways throughout the outflow. The increased amount of UV radiation in the inner region leads to photodissociation of parent species, releasing the otherwise deficient elements. We find an increased abundance in the inner region of all species not expected to be present assuming thermodynamic equilibrium chemistry, such as HCN in O-rich outflows, H 2 O in C-rich outflows, and NH 3 in both. Conclusions. A non-uniform density distribution directly influences the chemistry throughout the AGB outflow, both through the density structure itself and through its effect on the U...

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Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Cited by 20 publications

References 48 publications

The Maser-emitting Structure and Time Variability of the SiS Lines J = 14–13 and 15–14 in IRC+10216*

The Maser-emitting Structure and Time Variability of the SiS Lines J = 14–13 and 15–14 in IRC+10216*

The Chemistry of Cosmic Dust Analogs from C, C₂, and C₂H₂ in C-rich Circumstellar Envelopes

Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow

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Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Cited by 20 publications

References 48 publications

The Maser-emitting Structure and Time Variability of the SiS Lines J = 14–13 and 15–14 in IRC+10216*

The Maser-emitting Structure and Time Variability of the SiS Lines J = 14–13 and 15–14 in IRC+10216*

The Chemistry of Cosmic Dust Analogs from C, C2, and C2H2 in C-rich Circumstellar Envelopes

Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow

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The Chemistry of Cosmic Dust Analogs from C, C₂, and C₂H₂ in C-rich Circumstellar Envelopes