An ALMA view of CS and SiS around oxygen-rich AGB stars

Abstract

We aim to determine the distributions of molecular SiS and CS in the circumstellar envelopes of oxygen-rich asymptotic giant branch stars and how these distributions differ between stars that lose mass at different rates. In this study we analyse ALMA observations of SiS and CS emission lines for three oxygen-rich galactic AGB stars: IK Tau, with a moderately high mass-loss rate of $5\times 10^{-6}$M${}_{\odot }$ yr${}^{-1}$, and W Hya and R Dor with low mass loss rates of $\sim 1\times 10^{-7}$M${}_{\odot }$ yr${}^{-1}$. These molecules are usually more abundant in carbon stars but the high sensitivity of ALMA allows us to detect their faint emission in the low mass-loss rate AGB stars. The high spatial resolution of ALMA also allows us to precisely determine the spatial distribution of these molecules in the circumstellar envelopes. We run radiative transfer models to calculate the molecular abundances and abundance distributions for each star. We find a spread of peak SiS abundances with $\sim 10^{-8}$ for R Dor, $\sim 10^{-7}$ for W Hya, and $\sim 3\times 10^{-6}$ for IK Tau relative to H${}_2$. We find lower peak CS abundances of $\sim 7\times 10^{-9}$ for R Dor, $\sim 7\times 10^{-8}$ for W Hya and $\sim 4\times 10^{-7}$ for IK Tau, with some stratifications in the abundance distributions. For IK Tau we also calculate abundances for the detected isotopologues: C${}^{34}$S, ${}^{29}$SiS, ${}^{30}$SiS, Si${}^{33}$S, Si${}^{34}$S, ${}^{29}$Si${}^{34}$S, and ${}^{30}$Si${}^{34}$S. Overall the isotopic ratios we derive for IK Tau suggest a lower metallicity than solar.

16 pages

References in corpus (12)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• A close halo of large transparent grains around extreme red giant stars
• The millimeter IRAM-30m line survey toward IK Tau
• The abundance of SiS in circumstellar envelopes around AGB stars
• The wind of W Hya as seen by Herschel - I. The CO envelope
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• Sulphur-bearing molecules in AGB stars I: The occurrence of hydrogen sulfide
• The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars
• The wind of W Hya as seen by Herschel. II. The molecular envelope of W Hya
• First detection of photospheric depletion in the LMC
• The circumstellar envelope around the S-type AGB star W Aql Effects of an eccentric binary orbit
• The Evolution Of Carbon, Sulphur, and Titanium Isotopes from High-Redshift to the Local Universe

Cited by in corpus (14)

• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
• SO and SiS Emission Tracing an Embedded Planet and Compact ${}^{12}$CO and ${}^{13}$CO Counterparts in the HD 169142 Disk
• Dust-gas chemistry in AGB outflows: Chemical modelling of dust-gas chemistry within AGB outflows I. Effect on the gas-phase chemistry
• The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars
• ATOMIUM: Molecular inventory of 17 oxygen-rich evolved stars observed with ALMA
• An ALMA view of SO and SO${}_2$ around oxygen-rich AGB stars
• ATOMIUM: Halide molecules around the S-type AGB star W Aquilae
• Chemical modelling of dust-gas chemistry within AGB outflows -- II. Effect of the dust-grain size distribution
• Morpho-kinematics of the circumstellar envelope of the AGB star R Dor: a global view
• The unusual 3D distribution of NaCl around the AGB star IK Tau
• First detection of silicon-bearing molecules in $\eta$ Car
• Multi-line study of the radial extent of SiO, CS, and SiS in AGB envelopes
• exoALMA XIX: Confirmation of Non-thermal Line Broadening in the DM Tau Protoplanetary Disk
• Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. II. Abundances and spatial distributions of CS