ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen
  rich M-type stars: Motivation, sample, calibration, and initial results
  This overview paper presents ATOMIUM, a Large Programme in Cycle 6 with the
Atacama Large Millimeter-submillimeter Array (ALMA). The goal of ATOMIUM is to
understand the dynamics and the gas phase and dust formation chemistry in the
winds of evolved asymptotic giant branch (AGB) and red supergiant (RSG) stars.
A more general aim is to identify chemical processes applicable to other
astrophysical environments. 17 oxygen-rich AGB and RSG stars spanning a range
in (circum)stellar parameters and evolutionary phases were observed in a
homogeneous observing strategy allowing for an unambiguous comparison. Data
were obtained between 213.83 and 269.71 GHz at high (0.025-0.050 arcsec),
medium (0.13-0.24 arcsec), and low (about 1 arcsec) angular resolution. The
sensitivity per 1.3 km/s channel was 1.5-5 mJy/beam. 13 molecules were
designated as primary molecules in the survey: CO, SiO, AlO, AlOH, TiO, TiO2,
HCN, SO, SO2, SiS, CS, H2O, and NaCl. The scientific motivation, survey design,
sample properties, data reduction, and an overview of the data products are
described; and we highlight one scientific result - the wind kinematics of the
ATOMIUM sources. The ATOMIUM sources often have a slow wind acceleration, and a
fraction of the gas reaches a velocity which can be up to a factor of two times
larger than previously reported terminal velocities assuming isotropic
expansion, and the wind kinematic profiles establish that the radial velocity
described by the momentum equation for a spherical wind structure cannot
capture the complexity of the velocity field. In 15 sources, some molecular
transitions other than 12CO v=0 J=2-1 reach a higher outflow velocity, with a
spatial emission zone that is often greater than 30 stellar radii, but much
less than the extent of CO. Binary interaction with a (sub)stellar companion
might (partly) explain the non-monotonic behaviour of the projected velocity
field.
