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A spectral line and imaging survey of the low mass-loss rate AGB star R Dor(Mdot ~ 1e-7 Msun/yr) and the high mass-loss rate AGB star IK Tau (Mdot ~5e-6Msun/yr) was made with ALMA between 335 and 362 GHz at a spatial resolution of~150 mas, corresponding to the locus of the main dust formation region of bothtargets. Some 200 spectral features from 15 molecules (and their isotopologues)were observed, including rotational lines in both the ground and vibrationallyexcited states. Detected species include the gaseous precursors of dust grainssuch as SiO, AlO, AlOH, TiO, and TiO2. We present a spectral atlas for bothstars and the parameters of all detected spectral features. A clear dichotomyfor the sulphur chemistry is seen: while CS, SiS, SO, and SO2 are abundantlypresent in IK Tau, only SO and SO2 are detected in R Dor. Also other speciessuch as NaCl, NS, AlO, and AlOH display a completely different behaviour. Fromsome selected species, the minor isotopologues can be used to assess theisotopic ratios. The channel maps of many species prove that both large andsmall-scale inhomogeneities persist in the inner wind of both stars in the formof blobs, arcs, and/or a disk. The high sensitivity of ALMA allows us to spotthe impact of these correlated density structures in the spectral lineprofiles. The spectral lines often display a half width at zero intensity muchlarger than expected from the terminal velocity, v_inf, previously derived forboth objects (36 km/s versus v_inf ~17.7 km/s for IK Tau and 23 km/s versusv_inf ~5.5 km/s for R Dor). Both a more complex 3D morphology and a moreforceful wind acceleration of the (underlying) isotropic wind can explain thistrend. The formation of fractal grains in the region beyond ~400 mas canpotentially account for the latter scenario. From the continuum map, we deducea dust mass of ~3.7e-7 Msun for IK Tau and ~2e-8 Msun for R Dor.

ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz