Full synthesis maps of circumstellar SiC2 in IRC + 10216

Gensheimer, P. D.; Likkel, L.; Snyder, L. E.

doi:10.1086/175186

Cited by 30 publications

(38 citation statements)

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“…Silicon dicarbide, SiC 2 , has been detected in the inner wind of IRC+10216 by mm interferometry with abundances that range from <5 × 10 −8 (Gensheimer et al 1995) to 5 × 10 −7 (Lucas et al 1995). Recent observations with HIFI onboard Herschel indicate a SiC 2 abundance with respect to H 2 of 2 × 10 −7 in the inner wind ).…”

Section: Sic 2 and Sicmentioning

confidence: 99%

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

Cherchneff

2012

A&A

120

133

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Aims. We model the chemistry of the inner wind of the carbon star IRC+10216 and consider the effects of periodic shocks induced by the stellar pulsation on the gas to follow the non-equilibrium chemistry in the shocked gas layers. We consider a very complete set of chemical families, including hydrocarbons and aromatics, hydrides, halogens, and phosphorous-bearing species. Our derived abundances are compared to those for the latest observational data from large surveys and the Herschel telescope. Methods. A semi-analytical formalism based on parameterised fluid equations is used to describe the gas density, velocity, and temperature from 1 R to 5 R . The chemistry is described using a chemical kinetic network of reactions and a set of stiff, ordinary, coupled differential equations is solved. Results. The shocks induce an active non-equilibrium chemistry in the dust formation zone of IRC+10216 where the collision destruction of CO in the post-shock gas triggers the formation of O-bearing species such as H 2 O and SiO. Most of the modelled molecular abundances agree very well with the latest values derived from Herschel data on IRC+10216. The hydrides form a family of abundant species that are expelled into the intermediate envelope. In particular, HF traps all the atomic fluorine in the dust formation zone. The halogens are also abundant and their chemistry is independent of the C/O ratio of the star. Therefore, HCl and other Cl-bearing species should also be present in the inner wind of O-rich AGB or supergiant stars. We identify a specific region ranging from 2.5 R to 4 R , where polycyclic aromatic hydrocarbons form and grow. The estimated carbon dust-to-gas mass ratio derived from the mass of aromatics formed ranges from 1.2 × 10 −3 to 5.8 × 10 −3 and agrees well with existing values deduced from observations. This aromatic formation region is situated outside hot layers where SiC 2 is produced as a bi-product of silicon carbide dust synthesis. The MgS grains can form from the gas phase but in lower quantities than those necessary to reproduce the strength of the 30 μm emission band. Finally, we predict that some molecular lines will show a flux variation with pulsation phase and time (e.g., H 2 O), while other species will not (e.g., CO). These variations merely reflect the non-equilibrium chemistry that destroys and reforms molecules over a pulsation period in the shocked gas of the dust formation zone.

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Section: Sic 2 and Sicmentioning

confidence: 99%

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

Cherchneff

2012

A&A

120

133

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“…A large number of observations of this star is available in the UBV filters (Mauron et al 2003), radio (Gensheimer et al 1995) and infrared (Weigelt et al 1998, and references therein). However, to our knowledge, no direct mid-infrared images have been published in the literature.…”

Section: Irc +10216mentioning

confidence: 99%

Dust temperature and density profiles in the envelopes of AGB and post-AGB carbon stars from mid-infrared observations

Lagadec¹,

Mékarnia²,

Pacheco³

et al. 2005

A&A

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Abstract. First mid-infrared images of a sample of AGB and post-AGB carbon stars (V Hya, IRC +10216, CIT 6 and Roberts 22) obtained at the ESO-La Silla Observatory (Chile) are reported. CIT 6 presents a cometary-like feature clearly seen in the 9.7 µm image, Roberts 22 shows an envelope slightly elongated in the north-east direction while images of V Hya and IRC +10216 are roughly spherically symmetric. Using an inversion technique, the dust emissivity was derived from the observed intensity profiles, allowing a determination of the grain temperature and density distributions inside the envelope for these stars. Dust masses and mass-loss rates were estimated for V Hya and IRC +10216. Our results are comparable to those obtained in previous studies if dust grains have dimensions in the range ∼0.01-0.2 µm. Color maps suggest the presence of temperature inhomogeneities in the central regions of the dust envelopes. In the case of V Hya, an eccentric hot point, whose direction coincides with the jet previously seen in [S II] emission, suggests that we are observing material ejected in a previous mass-loss event. Bipolar lobes are clearly seen in the color maps of Roberts 22 and IRC +10216.

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“…The diameter of the SiCC shell has been measured interferometrically by three groups to be about 40Љ (Takano, Saito, & Tsuji 1992;Gensheimer, Likkel, & Snyder 1995;Guélin, Lucas, & Neri 1996). For want of interferometric data, we will assume that the shells of SiC 3 and SiC 4 also have a diameter of 40Љ.…”

mentioning

confidence: 99%

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

Apponi

McCarthy

Gottlieb

et al. 1999

The Astrophysical Journal

147

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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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Full synthesis maps of circumstellar SiC2 in IRC + 10216

Cited by 30 publications

References 0 publications

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars

Dust temperature and density profiles in the envelopes of AGB and post-AGB carbon stars from mid-infrared observations

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

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