The Abundance of C<sub>2</sub>H<sub>4</sub> in the Circumstellar Envelope of IRC+10216

Fonfría, J. P.; Hinkle, Kenneth H.; Cernicharo, J.; Richter, Matthew J.; Agúndez, M.; Wallace, L.

doi:10.3847/1538-4357/835/2/196

Cited by 21 publications

(27 citation statements)

References 63 publications

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“…The intensity of their absorption component suggests a column density ≲ 10 16 cm −2 . These line profiles are compatible with a molecule formed either in the outer envelope or as close to the star as ≃ 10 – 15 R ⋆ , as it occurs with C 2 H 4 (Fonfría et al 2017). C 2 H 4 shows absorption features produced by two different excitation populations compatible with a molecular species arising in the dust formation zone ( r ≲ 20 R ⋆ ; Fonfría et al 2008), where the gas is still being accelerated and the kinetic temperature is above ≃ 400 K, and a significant absorption produced in the colder shells of the outer envelope.…”

Section: Resultssupporting

confidence: 61%

“…This effect is difficult to quantify so, to a first approximation, we can place the shell where the observed lines are formed by using the kinetic temperature radial profile recently derived by Guélin et al (2017) from high spatial resolution data of 12 CO ( T k ≃ 257( r/ 0.8) −0.675 K, if r ≲ 15 ″ and T k ≃ 35 K beyond). Hence, the cold population of C 4 H 2 is at 10.0−1.8+2.7 arcsec from the star 500−90+140R⋆=(1.8−0.3+0.5)×1016cm, if R⋆=0·"02=3.7×1013cm; Ridgway & Keady 1988; Fonfría et al 2017) while the hot population arises at 0.40−0.14+0.30 arcsec from the star (20−7+15R⋆=(7−3+6)×1014cm). We estimate the C 4 H 2 abundance with respect to H 2 to be 6 × 10 −7 and 8 × 10 −6 for the hot and cold populations, respectively, with an uncertainty roughly of a factor of 2.…”

Section: Resultsmentioning

confidence: 98%

“…Several authors have demonstrated that the circumstellar chemistry can be significantly modified if a higher density, higher temperature photochemistry and clumpiness are considered (Woods et al 2003; Redman et al 2003; Cernicharo 2004; Agúndez et al 2010). In this scenario, the abundance of C 4 H 2 is naturally explained at the same time than the existence of H 2 O in the envelope of a C-rich star (Melnick et al 2001; Agúndez & Cernicharo 2006; Agúndez et al 2010; Neufeld et al 2013) and the discovery of vibrationally excited C 4 H and C 2 H 4 as close to the star as ≃ 10 R ⋆ (Yamamoto et al 1987; Cooksy et al 2015; Fonfría et al 2017).…”

Section: Discussionmentioning

confidence: 99%

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Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Fonfría

Agúndez

Cernicharo

et al. 2018

ApJ

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We present the detection of C 4 H 2 for first time in the envelope of the C-rich AGB star IRC+10216 based on high spectral resolution mid-IR observations carried out with the Texas Echelon-cross-Echelle Spectrograph (TEXES) mounted on the Infrared Telescope Facility (IRTF). The obtained spectrum contains 24 narrow absorption features above the detection limit identified as lines of the ro-vibrational C 4 H 2 band ν 6 + ν 8 (σ + u ). The analysis of these lines through a ro-vibrational diagram indicates that the column density of C 4 H 2 is (2.4 ± 1.5) × 10 16 cm −2 . Diacetylene is distributed in two excitation populations accounting for 20 and 80% of the total column density and with rotational temperatures of 47 ± 7 and 420 ± 120 K, respectively. This two-folded rotational temperature suggests that the absorbing gas is located beyond 0. 4 20R from the star with a noticeable cold contribution outwards from 10 500R . This outer shell matches up with the place where cyanoacetylenes and carbon chains are known to form due to the action of the Galactic dissociating radiation field on the neutral gas coming from the inner layers of the envelope.

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Section: Resultssupporting

confidence: 61%

Section: Resultsmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

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Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Fonfría

Agúndez

Cernicharo

et al. 2018

ApJ

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“…Hydrocarbons such as CH 4 and C 2 H 4 are calculated to be quite abundant at 10 R * in C-type atmospheres (see Fig. 2) and have been observed in IRC +10216 with abundances of about the predicted ones (Keady & Ridgway 1993;Fonfría et al 2017). Furthermore, carbon dioxide is calculated with a mole fraction in the range 10 −8 -10 −6 in M-type atmospheres (see Fig.…”

Section: Successesmentioning

confidence: 94%

Chemical equilibrium in AGB atmospheres: successes, failures, and prospects for small molecules, clusters, and condensates

Agúndez

Martínez

Andrés

et al. 2020

A&A

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107

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Chemical equilibrium has proven extremely useful for predicting the chemical composition of AGB atmospheres. Here we use a recently developed code and an updated thermochemical database that includes gaseous and condensed species involving 34 elements to compute the chemical equilibrium composition of AGB atmospheres of M-, S-, and C-type stars. We include for the first time Ti x C y clusters, with x = 1-4 and y = 1-4, and selected larger clusters ranging up to Ti 13 C 22 , for which thermochemical data are obtained from quantum-chemical calculations. Our main aims are to systematically survey the main reservoirs of each element in AGB atmospheres, review the successes and failures of chemical equilibrium by comparing it with the latest observational data, identify potentially detectable molecules that have not yet been observed, and diagnose the most likely gas-phase precursors of dust and determine which clusters might act as building blocks of dust grains. We find that in general, chemical equilibrium reproduces the observed abundances of parent molecules in circumstellar envelopes of AGB stars well. There are, however, severe discrepancies of several orders of magnitude for some parent molecules that are observed to be anomalously overabundant with respect to the predictions of chemical equilibrium. These are HCN, CS, NH 3 , and SO 2 in M-type stars, H 2 O and NH 3 in S-type stars, and the hydrides H 2 O, NH 3 , SiH 4 , and PH 3 in C-type stars. Several molecules have not yet been observed in AGB atmospheres but are predicted with nonnegligible abundances and are good candidates for detection with observatories such as ALMA. The most interesting ones are SiC 5 , SiNH, SiCl, PS, HBO, and the metal-containing molecules MgS, CaS, CaOH, CaCl, CaF, ScO, ZrO, VO, FeS, CoH, and NiS. In agreement with previous studies, the first condensates predicted to appear in C-rich atmospheres are found to be carbon, TiC, and SiC, while Al 2 O 3 is the first major condensate expected in O-rich outflows. According to our chemical equilibrium calculations, the gas-phase precursors of carbon dust are probably acetylene, atomic carbon, and/or C 3 , while for silicon carbide dust, the most likely precursors are the molecules SiC 2 and Si 2 C. In the case of titanium carbide dust, atomic Ti is the major reservoir of this element in the inner regions of AGB atmospheres, and therefore it is probably the main supplier of titanium during the formation of TiC dust. However, chemical equilibrium predicts that large titanium-carbon clusters such as Ti 8 C 12 and Ti 13 C 22 become the major reservoirs of titanium at the expense of atomic Ti in the region where condensation of TiC is expected to occur. This suggests that the assembly of large Ti x C y clusters might be related to the formation of the first condensation nuclei of TiC. In the case of Al 2 O 3 dust, chemical equilibrium indicates that atomic Al and the carriers of Al-O bonds AlOH, AlO, and Al 2 O are the most likely gas-phase precursors.

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“…The model of the SiS(14 – 13) line presented in Section 2 was achieved with an improved version of the code initially developed by Fonfría et al (2008) to calculate the emission of a spherically symmetric circumstellar envelope composed of dust and radially expanding gas (Fonfría et al 2011, 2015, 2017a). The new version allows us to deal with 3D asymmetric envelopes.…”

Section: Modelingmentioning

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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The Abundance of C₂H₄ in the Circumstellar Envelope of IRC+10216

Cited by 21 publications

References 63 publications

Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Chemical equilibrium in AGB atmospheres: successes, failures, and prospects for small molecules, clusters, and condensates

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

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The Abundance of C2H4 in the Circumstellar Envelope of IRC+10216

Cited by 21 publications

References 63 publications

Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Carbon Chemistry in IRC+10216: Infrared Detection of Diacetylene

Chemical equilibrium in AGB atmospheres: successes, failures, and prospects for small molecules, clusters, and condensates

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

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The Abundance of C₂H₄ in the Circumstellar Envelope of IRC+10216