Recent mass ejection from AGB star W Hya
  We analyse archival ALMA observations of two molecular line emissions,
$^{12}$CO(3-2) and $^{29}$SiO(8-7), from oxygen-rich AGB star W Hya. Together
with results of earlier VLT observations at visible and infrared wavelengths,
our results suggest a two-component picture of the morpho-kinematics of the
circumstellar envelope (CSE), one stable over time, at the scale of centuries,
and the other variable, at the scale of years. The stable component consists of
an approximately spherical shell of gas and dust expanding radially to a
terminal velocity of $\sim$5 km s$^{-1}$ at a distance of $\sim$30 au from the
star. It is found to display comparable features as seen in the CSE of R Dor, a
star similar to W Hya. The variable component projects on the plane of the sky
over a region confined to the neighbourhood of the star and elongated toward
the north. Its very high density and sudden acceleration suggest an
interpretation in terms of mass ejection initiated a few years ago. We discuss
its properties in relation with earlier observations of dust formation in the
same region. Our results have an impact on the evidence published earlier for
the presence of CO masers. They favour an interpretation in terms of convective
cell ejections playing the main role in the generation of the nascent wind, the
stable component of the CSE being seen as the result of many successive such
events occurring in different directions at short time intervals.
