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Using ALMA, we observed the stellar wind of two oxygen-rich Asymptotic GiantBranch (AGB) stars, IK Tau and R Dor, between 335 and 362 GHz. One aim was todetect metal oxides and metal hydroxides (AlO, AlOH, FeO, MgO, MgOH), some ofwhich are thought to be direct precursors of dust nucleation and growth. Wereport on the potential first detection of FeO (v=0, Omega=4, J=11-10) in RDor(mass-loss rate, Mdot, ~1e-7 Msun/yr). The presence of FeO in IK Tau (Mdot~5e-6Msun/yr) cannot be confirmed due to a blend with 29SiS, a molecule that isabsent in R Dor. The detection of AlO in R Dor and of AlOH in IK Tau wasreported earlier by Decin et al. (2017). All other metal oxides and hydroxides,as well as MgS, remain undetected. We derive a column density N(FeO) of1.1+/-0.9e15 cm^{-2} in R Dor, or a fractional abundance [FeO/H]~1.5e-8accounting for non-LTE effects. The derived fractional abundance [FeO/H] is afactor ~20 larger than conventional gas-phase chemical kinetic predictions.This discrepancy may be partly accounted for by the role of vibrationallyexcited OH in oxidizing Fe, or may be evidence for other currently unrecognisedchemical pathways producing FeO. Assuming a constant fractional abundancew.r.t. H_2, the upper limits for the other metals are [MgO/H_2] <5.5e-10 (RDor) and <7e-11 (IK Tau), [MgOH/H_2] <9e-9 (R Dor) and <1e-9 (IK Tau),[CaO/H_2] <2.5e-9 (R Dor) and <1e-10 (IK Tau), [CaOH/H_2] <6.5e-9 (R Dor) and<9e-10 (IK Tau), and [MgS/H_$] <4.5e-10 (R Dor) and <6e-11 (IK Tau). Theretrieved upper limit abundances for these latter molecules are in accord withthe chemical model predictions.

Constraints on metal oxide and metal hydroxide abundances in the winds of AGB stars - Potential detection of FeO in R Dor