Submillimeter‐ and Millimeter‐Wavelength Observations of SiO and HCN in Circumstellar Envelopes of AGB Stars

Bieging, John H.; Shaked, S.; Gensheimer, P. D.

doi:10.1086/317129

Cited by 60 publications

(79 citation statements)

References 26 publications

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“…They are the daughter species of parent molecules such as HCN and HCCH produced at LTE. In addition, shock waves in the shell, caused by thermal pulses, may influence abundances (19,20).…”

Section: The Chemical Environment Of Circumstellar Shellsmentioning

confidence: 99%

The chemistry in circumstellar envelopes of evolved stars: Following the origin of the elements to the origin of life

Ziurys

2006

Proc. Natl. Acad. Sci. U.S.A.

268

207

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“…They are the daughter species of parent molecules such as HCN and HCCH produced at LTE. In addition, shock waves in the shell, caused by thermal pulses, may influence abundances (19,20).…”

Section: The Chemical Environment Of Circumstellar Shellsmentioning

confidence: 99%

The chemistry in circumstellar envelopes of evolved stars: Following the origin of the elements to the origin of life

Ziurys

2006

Proc. Natl. Acad. Sci. U.S.A.

268

207

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“…Later on, observations were (re)-analyzed based on a non-LTE (non-local thermodynamic equilibrium) radiative transfer model (e.g. Bieging et al 2000;Teyssier et al 2006;Schöier et al 2007a). In this study we will go one step further and abandon or improve few of the assumptions still made in many non-LTE analyses.…”

Section: Introductionmentioning

confidence: 99%

Circumstellar molecular composition of the oxygen-rich AGB star IK Tauri

Decin

Beck²,

Brünken

et al. 2010

A&A

103

212

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Context. The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflow from these stars creates a circumstellar envelope in which a rich gas-phase chemistry takes place. Complex shock-induced nonequilibrium chemistry takes place in the inner wind envelope, dust-gas reactions and ion-molecule reactions alter the abundances in the intermediate wind zone, and the penetration of cosmic rays and ultraviolet photons dissociates the molecules in the outer wind region. Aims. Little observational information exists on the circumstellar molecular abundance stratifications of many molecules. Furthermore, our knowledge of oxygen-rich envelopes is not as profound as for the carbon-rich counterparts. The aim of this paper is therefore to study the circumstellar chemical abundance pattern of 11 molecules and isotopologs ( 12 CO, 13 CO, SiS, 28 SiO, 29 SiO, 30 SiO, HCN, CN, CS, SO, SO 2 ) in the oxygen-rich evolved star IK Tau. Methods. We have performed an in-depth analysis of a large number of molecular emission lines excited in the circumstellar envelope around IK Tau. The analysis is done based on a non-local thermodynamic equilibrium (non-LTE) radiative transfer analysis, which calculates the temperature and velocity structure in a self-consistent way. The chemical abundance pattern is coupled to theoretical outer wind model predictions including photodestruction and cosmic ray ionization. Not only the integrated line intensities, but also the line shapes are used as diagnostic tool to study the envelope structure. Results. The deduced wind acceleration is much slower than predicted from classical theories. SiO and SiS are depleted in the envelope, possibly due to the adsorption onto dust grains. For HCN and CS a clear difference with respect to inner wind non-equilibrium predictions is found, either indicating uncertainties in the inner wind theoretical modeling or the possibility that HCN and CS (or the radical CN) participate in the dust formation. The low signal-to-noise profiles of SO and CN prohibit an accurate abundance determination; the modeling of high-excitation SO 2 lines is cumbersome, possibly related to line misidentifications or problems with the collisional rates.

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“…It is particularly strong towards IRC +10216 and CIT6 (Lucas & Cernicharo 1989;Schilke et al 2000;Schilke & Menten 2003;Avery et al 1994;Bieging et al 2000). Interpretating it is complicated by a wealth This work was based on observations carried out with the IRAM 30-m telescope.…”

Section: Introductionmentioning

confidence: 99%

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

Cernicharo

Agúndez

Kahane

et al. 2011

A&A

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We report the detection in IRC +10216 of 63 rotational transitions of HCN, most of them with quantum numbers J = 3-2, pertaining to 28 different vibrational states with energies up to 10 700 K (ν 1 +3ν 2 +ν 3 ). Some of the transitions were also observed for the rare isotopologue H 13 CN. The observations were carried out with the IRAM 30-m telescope. The HCN lines with level energies above 5000 K arise within 1.5 stellar radius from the photosphere. Their intensities imply a vibrational temperature of T vib 2400 K and a fractional HCN abundance relative to H 2 , x(HCN) = 5-7 × 10 −5 . These high-energy levels are mainly populated by photospheric radiation, and their vibrational temperature yields a direct measurement of the stellar photospheric temperature. The lines with energy levels between 2000 and 5000 K yield T vib 1300 K and x(HCN) 0.8-2 × 10 −5 . They are radiatively excited and arise from a shell extending between 1.5 and 5 stellar radii. Finally, the lines from the low-energy vibrational states (<2000 K) trace a larger region of the envelope (5-28 stellar radii) with T vib = 400-600 K and x(HCN) = 4-6× 10 −6 . They are strongly affected by mid and near-infrared pumping. The line widths increase from 5 km s −1 near the 2400 K photosphere, to 19 km s −1 in the warm 400 K shell. This provides a unique insight into the physical conditions of the gas acceleration and dust formation region.

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Submillimeter‐ and Millimeter‐Wavelength Observations of SiO and HCN in Circumstellar Envelopes of AGB Stars

Cited by 60 publications

References 26 publications

The chemistry in circumstellar envelopes of evolved stars: Following the origin of the elements to the origin of life

The chemistry in circumstellar envelopes of evolved stars: Following the origin of the elements to the origin of life

Circumstellar molecular composition of the oxygen-rich AGB star IK Tauri

Probing the dust formation region in IRC +10216 with the high vibrational states of hydrogen cyanide

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