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 .