Circumstellar molecular composition of the oxygen-rich AGB star IK~Tau: II. In-depth non-LTE chemical abundance analysis

Abstract

Aims: Little information exists on the circumstellar molecular abundance stratifications of many molecules. The aim is 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. The SiO isotopic ratios (${}^{29}$SiO/${}^{28}$SiO and ${}^{30}$SiO/${}^{28}$SiO) point toward an enhancement in ${}^{28}$SiO compared to results of classical stellar evolution codes. Predictions for H${}_2$O lines in the spectral range of the Herschel/HIFI mission are performed. [abbreviated]

24 pagees, accepted for publication in Astronomy & Astrophysics

References in corpus (9)

• Too little radiation pressure on dust in the winds of oxygen-rich AGB stars
• A spectral line survey in the 2 mm and 1.3 mm windows toward the carbon rich envelope of IRC +10216
• SiO in C-rich circumstellar envelopes of AGB stars: effects of non-LTE chemistry and grain adsorption
• The distribution of SiO in the circumstellar envelope around IRC+10216
• The variable mass loss of the AGB star WX Psc as traced by the CO J=1-0 through 7-6 lines and the dust emission
• Circumstellar molecular composition of the oxygen-rich AGB star IK Tau: I. Observations and LTE chemical abundance analysis
• Circumstellar water vapour in M-type AGB stars: Constraints from H2O(1_10 - 1_01) lines obtained with Odin
• Water vapor emission from IRC+10216 and other carbon-rich stars: model predictions and prospects for multitransition observations
• The distribution of H13CN in the circumstellar envelope around IRC+10216

Cited by in corpus (38)

• Dust formation in the oxygen-rich AGB star IK Tau
• Warm water vapour in the sooty outflow from a luminous carbon star
• PO and PN in the wind of the oxygen-rich AGB star IK Tau
• The millimeter IRAM-30m line survey toward IK Tau
• Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tau as seen by Herschel/HIFI
• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• The wind of W Hya as seen by Herschel - I. The CO envelope
• Sulphur molecules in the circumstellar envelopes of M-type AGB stars
• A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling
• Resolving the extended atmosphere and the inner wind of Mira ($o$ Ceti) with long ALMA baselines
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow
• On the physical structure of IRC+10216. Ground-based and Herschel observations of CO and CCH
• Wind morphology around cool evolved stars in binaries: the case of slowly accelerating oxygen-rich outflows
• Silicon in the dust formation zone of IRC +10216 as observed with PACS and SPIRE on board Herschel
• Herschel/HIFI deepens the circumstellar NH3 enigma
• Search for aluminium monoxide in the winds of oxygen-rich AGB stars
• SPH modelling of companion-perturbed AGB outflows including a new morphology classification scheme
• The wind of W Hya as seen by Herschel. II. The molecular envelope of W Hya
• The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars
• An ALMA view of CS and SiS around oxygen-rich AGB stars
• H2O vapor excitation in dusty AGB envelopes. A PACS view of OH 127.8+0.0
• Constraints on metal oxide and metal hydroxide abundances in the winds of AGB stars - Potential detection of FeO in R Dor
• Dust-gas chemistry in AGB outflows: Chemical modelling of dust-gas chemistry within AGB outflows I. Effect on the gas-phase chemistry
• An ALMA view of SO and SO${}_2$ around oxygen-rich AGB stars
• Late Stages of Stellar Evolution - Herschel's contributions
• ALMA observations of the nearby AGB star L${}_2$ Puppis. II. Gas disk properties derived from ${}^{12}$CO and ${}^{13}$CO $J=$3$-$2 emission
• Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars
• Observational evidence for composite grains in an AGB outflow: MgS in the extreme carbon star LL Peg
• Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes -- I. The case of hydrogen cyanide
• Arcsecond resolution mapping of Sulfur Dioxide emission in the circumstellar envelope of VY Canis Majoris
• Chemical modelling of dust-gas chemistry within AGB outflows III. Photoprocessing of the ice and return to the ISM
• Chemical modelling of dust-gas chemistry within AGB outflows -- II. Effect of the dust-grain size distribution
• A HIFI preview of warm molecular gas around chi Cyg : first detection of H2O emission toward an S-type AGB star
• Model of the vibrationally excited H${}_2$O maser at 658 GHz in circumstellar envelopes around asymptotic giant branch stars
• H12CN and H13CN excitation analysis in the circumstellar outflow of R Scl
• Mapping circumstellar magnetic fields of late-type evolved stars with the Goldreich-Kylafis effect: CARMA observations at $\lambda 1.3$ mm of R Crt and R Leo
• A molecular line survey of a sample of AGB stars and planetary nebulae