Identification of the SiCC radical toward IC +10216 - The first molecular ring in an astronomical source

Thaddeus, P.; Cummins, S. E.; Linke, R. A.

doi:10.1086/184330

Cited by 276 publications

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“…We obtain an upper limit to its column density of 3.5 × 10 13 cm −2 and an abundance ratio N(SiO)/N(SiC 2 ) > ∼ 211. This molecule and its isotopologs have also been detected towards IRC+101216 by Thaddeus et al (1984) Ohishi et al (1989) in the envelope of IRC+10216. For this molecule we calculated an upper limit to its column density in Orion KL of 3.5 × 10 12 cm −2 , and a ratio N(SiO)/N(SiC 4 ) > ∼ 2114.…”

Section: Other Silicon-bearing Moleculesmentioning

confidence: 74%

A line-confusion limited millimeter survey of Orion KL

Tercero

Vincent

Cernicharo

et al. 2011

A&A

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Aims. We present a study of the silicon-bearing species detected in a line-confusion limited survey towards Orion KL performed with the IRAM 30-m telescope. The analysis of the line survey is organized by families of molecules. Our aim is to derive physical and chemical conditions for each family taking all observed lines into account from all isotopologs of each species. The large number of transitions in different vibrationally excited states covered by our data, which range from 80 to 280 GHz, let us provide reliable source-average column densities (hence, isotopolog abundances and vibrational temperatures) for the detected molecules. In addition, we provide a wide study of the physical properties of the source based on the different spectral components found in the emission lines. Methods. We modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between large velocity gradient (LVG) and local thermodynamic equilibrium (LTE) approximations depending on the physical conditions of the gas. We used appropriate collisional rates for the LVG calculations. To qualitatively investigate the origin of the SiS and SiO emissions in Orion KL we ran a grid of chemical models.Results. For the v = 1 state of SiO, we detected the J = 2−1 line and, for the first time in this source, emission in the J = 4−3 transition, both of them showing a strong masering effect. For SiO v = 0, we detected 28 SiO, 29 SiO, and 30 SiO; in addition, we have mapped the J = 5−4 SiO line. For SiS, we have detected the main species, 29 SiS, and SiS v = 1. Unlikely other species detected in Orion KL (IRc2), the emission peak of SiS appears at a velocity of 15.5 km s −1 . A study of the 5−4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud. We derive an SiO/SiS column density ratio of 13 in the plateau component, four times lower than the cosmic O/S ratio 48. In addition, we provide upper limits to the column density of several non-detected silicon-bearing species. The results of our chemical models show that while it is possible to reproduce SiO in the gas phase (as well as on the grains), SiS is a product of surface reactions, most likely involving direct reactions of sulfur with silicon.

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Section: Other Silicon-bearing Moleculesmentioning

confidence: 74%

A line-confusion limited millimeter survey of Orion KL

Tercero

Vincent

Cernicharo

et al. 2011

A&A

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“…Take SiC 2 as an example. The cited column density for this molecule in Table 3 is 2.0 ×10 14 cm −2 (Thaddeus et al 1984). However, according to a more recent study by Cernicharo et al (2010) employing high quality Herschel/HIFI spectra an average column density of ∼6.4 × 10 15 cm −2 was found.…”

Section: Column Densitymentioning

confidence: 80%

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

Millar

Walsh

et al. 2014

A&A

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Context. The envelopes of asymptotic giant branch (AGB) stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N 2 and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N 2 has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. Aims. For the first time, we use accurate N 2 and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. Methods. We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N 2 photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. Results. The transition of N 2 → N (also, CO → C → C + ) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, C n N (n = 1, 3, 5), C n N − (n = 1, 3, 5), HC n N (n = 1, 3, 5, 7, 9), H 2 CN and CH 2 CN. Conclusions. The chemistry of many species is directly or indirectly affected by the photodissociation of N 2 and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N 2 and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.

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“…It has recently been detected for the first time in this laboratory, and its rotational spectrum has been measured to high precision in both the centimeterand millimeter-wave bands Apponi et al 1999). Observing at the laboratory frequencies, we have now detected, with the NRAO 3 12 m telescope on Kitt Peak, seven transitions of this unusual molecular ring in the rich molecular envelope of the evolved carbon star IRC ϩ10216, which is a source where three silicon-carbon molecules have already been detected: the diatomic radical SiC (Cernicharo et al 1989), the closed-shell ionic ring SiCC (Thaddeus, Cummins, & Linke 1984), and the closed-shell linear chain SiC 4 (Ohishi et al 1989). Rhomboidal SiC 3 is the fifth and largest cyclic molecule so far identified in space (after SiCC, c-C H , c-C H, and ethylene oxide c-C H O [Dickens et 3 2 3 2 4 al.…”

Section: ϫ2mentioning

confidence: 96%

Astronomical Detection of Rhomboidal S[CLC]i[/CLC]C[TINF]3[/TINF]

Apponi

McCarthy

Gottlieb

et al. 1999

The Astrophysical Journal

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Seven rotational transitions of SiC 3 , a planar, highly polar ring molecule, have been detected in the millimeterwave band in the expanding envelope of the evolved carbon star IRC ϩ10216. On the assumption that SiC 3 has the same 40Љ diameter shell as SiCC, the mean column density of SiC 3 is cm . The rotational 12 Ϫ24.3 # 10 excitation of SiC 3 is similar to that of SiCC, with a low rotational temperature within the K-stacks of 10-20 K and a high rotational temperature across the K-stacks of roughly 50 K, which is probably close to the kinetic temperature of the shell.Subject headings: ISM: molecules -line: identification -molecular data -molecular processesradio lines: ISMThe most stable molecule with the elemental formula SiC 3 has been calculated to be the rhomboidal isomer with a transannular bond, as shown in Figure 1 (Alberts, Grev, & Schaefer 1990;Gomei et al. 1997). It has recently been detected for the first time in this laboratory, and its rotational spectrum has been measured to high precision in both the centimeterand millimeter-wave bands Apponi et al. 1999). Observing at the laboratory frequencies, we have now detected, with the NRAO 3 12 m telescope on Kitt Peak, seven transitions of this unusual molecular ring in the rich molecular envelope of the evolved carbon star IRC ϩ10216, which is a source where three silicon-carbon molecules have already been detected: the diatomic radical SiC al. 1997], the only stable ring so far detected).The observations are summarized in Table 1, and four of the lines are shown in Figure 2. The uncertainties in our rest frequencies are only 0.3 km s or less and, therefore, negligible Ϫ1 relative to both the width of the lines in the molecular shell of IRC ϩ10216 (28 km s ) and the spectral resolution of our Ϫ1 observations (3-4 km s ). Lines of nearly all molecules in Ϫ1 this source lie at a radial velocity of Ϫ km s , which, Ϫ126 ‫ע‬ 1 as Table 1 shows, to within the observational uncertainties, is the velocity of all the lines attributed to SiC 3 . Because the average interval between unidentified lines as strong as 5 mK in this part of the spectrum of IRC ϩ10216 is at least 30 MHz in frequency, or 100 km s in velocity, the probability that Ϫ1 any one of our seven lines is misidentified is a few percent at most, and the joint probability that all are misidentified is extremely small. In spite of its fairly weak lines, is one of the more securely identified molecules in IRC ϩ10216.The observations were done with the 12 m NRAO telescope on Kitt Peak during 1998 December when the sky was clear and the zenith opacity of water vapor at 225 GHz was generally 0.2 or less. The dual polarization SIS receiver used for the observations had a single-sideband system temperature of 200 K or less, atmospheric emission included. Pointing was checked every few hours against Saturn or 3C 273 and was found to be good to 10Љ. Spectra were taken by beam switching with the telescope's nutating subreflector at 1.25 Hz, with an angular throw of 4Ј. Two filter banks, each of 256...

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Identification of the SiCC radical toward IC +10216 - The first molecular ring in an astronomical source

Cited by 276 publications

References 0 publications

A line-confusion limited millimeter survey of Orion KL

A line-confusion limited millimeter survey of Orion KL

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

Astronomical Detection of Rhomboidal S[CLC]i[/CLC]C[TINF]3[/TINF]

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Identification of the SiCC radical toward IC +10216 - The first molecular ring in an astronomical source

Cited by 276 publications

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A line-confusion limited millimeter survey of Orion KL

A line-confusion limited millimeter survey of Orion KL

Photodissociation and chemistry of N2in the circumstellar envelope of carbon-rich AGB stars

Astronomical Detection of Rhomboidal S[CLC]i[/CLC]C[TINF]3[/TINF]

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Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars