Mira Ceti, atypical archetype
  With the aim of unraveling the complexity of the morpho-kinematics of the
circumstellar envelope (CSE) of Mira Ceti, we review, extend and in some cases
revisit ALMA millimeter observations of the emission of the SiO(5-4) and
CO(3-2) molecular lines. In addition, we present a detailed analysis of the
optically thin $^{13}$CO(3-2) emission, which provides several important new
results. In agreement with observations at infrared and visible wavelengths, we
give evidence for confinement and probably rotation of a dense gas volume
within $\sim$50 au from the star and for a large SiO line-width within $\sim$15
au. We show that the mass loss process is episodic and takes the form of clumps
having a very low SiO/CO abundance ratio compared with similar oxygen-rich long
period variables, probably a result of depletion on dust grains and
photo-dissociation. We evaluate the mass loss rate associated with the main
clumps and compare it with values obtained from single dish observations. We
argue that the SiO emission observed in the south-western quadrant is not
related to the mechanism of generation of the nascent wind but to a mass
ejection that occurred eleven years before the observations. We remark that
Mira Ceti is not a good archetype in terms of its wind: models aiming at
describing the very complex gas-dust chemistry in action in the CSE of
oxygen-rich AGB stars may find it difficult to account for its peculiar
features, small variations in the parameters deciding when and where mass loss
can proceed significantly.
