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Aims: We aim to determine the abundances of SiO, CS, SiS, SO, and SO$_2$ in alarge sample of oxygen-rich AGB envelopes covering a wide range of mass lossrates to investigate the potential role that these molecules could play in theformation of dust in these environments.  Methods:We surveyed a sample of 30 oxygen-rich AGB stars in the $\lambda$ 2mm band using the IRAM 30m telescope. We performed excitation and radiativetransfer calculations based on the LVG method to model the observed lines ofthe molecules and to derive their fractional abundances in the observedenvelopes.  Results:We detected SiO in all 30 targeted envelopes, as well as CS, SiS, SO,and SO$_2$ in 18, 13, 26, and 19 sources, respectively. Remarkably, SiS is notdetected in any envelope with a mass loss rate below $10^{-6}$ M$_{\odot}$yr$^{-1}$, whereas it is detected in all envelopes with mass loss rates abovethat threshold. From a comparison with a previous, similar study on C-richsources, it becomes evident that the fractional abundances of CS and SiS show amarked differentiation between C-rich and O-rich sources, being two orders ofmagnitude and one order of magnitude more abundant in C-rich sources,respectively, while the fractional abundance of SiO turns out to be insensitiveto the C/O ratio. The abundance of SiO in O-rich envelopes behaves similarly toC-rich sources, that is, the denser the envelope the lower its abundance. Asimilar trend, albeit less clear than for SiO, is observed for SO in O-richsources.  Conclusions: The marked dependence of CS and SiS abundances on the C/O ratioindicates that these two molecules form more efficiently in C- than O-richenvelopes. The decline in the abundance of SiO with increasing envelope densityand the tentative one for SO indicate that SiO and possibly SO act as gas-phaseprecursors of dust in circumstellar envelopes around O-rich AGB stars.

The abundance of S- and Si-bearing molecules in O-rich circumstellar envelopes of AGB stars