This paper describes observations of a new phenomenon in evolved mass-losing
AGB stars: the presence of two winds with different expansion velocities.
CO(2-1) and CO(3-2) line emission was observed for 45 AGB stars at high
velocity resolution and double winds found in 20% of the sample. Highly
asymmetric lines were found in six other stars. The data tentatively suggest
that double winds occur when the star undergoes a change (pulsational mode,
chemical composition) and that the very narrow components represent the onset
of a new phase of mass loss.Comment: 53 pages, plain TeX, 16 figures in file figs.p