Context :

Aims : Many aspects of the evolutionary phase in which Asymptotic Giant Branch stars ( AGB stars ) are in transition to become Planetary Nebulae ( PNe ) are still poorly understood .
An important question is how the circumstellar envelopes of AGB stars switch from spherical symmetry to the axially symmetric structures frequently observed in PNe .
In many cases there is clear evidence that the shaping of the circumstellar envelopes of PNe is linked to the formation of jets/collimated winds and their interaction with the remnant AGB envelope .
Because of the short evolutionary time , objects in this phase are rare , but their identification provides valuable probes for testing evolutionary models .

Methods : We have observed ( sub ) millimeter CO rotational transitions with the APEX telescope in a small sample of stars hosting high-velocity OH and water masers .
These targets are supposed to have recently left the AGB , as indicated by the presence of winds traced by masers , with velocities larger than observed during that phase .
We have carried out observations of several CO lines , ranging from \mathrm { J } = 2 - 1 up to \mathrm { J } = 7 - 6 .

Results : In IRAS 15452 - 5459 we detect a fast molecular outflow in the central region of the nebula and estimate a mass-loss rate between 1.2 \times 10 ^ { -4 } M _ { \odot } yr ^ { -1 } ( assuming optically thin emission ) and 4.9 \times 10 ^ { -4 } M _ { \odot } yr ^ { -1 } ( optically thick emission ) .
We model the SED of this target taking advantage of our continuum measurement at 345 GHz to constrain the emission at long wavelengths .
For a distance of 2.5 kpc , we estimate a luminosity of 8000 L _ { \odot } and a dust mass of \sim 0.01 M _ { \odot } .
Through the flux in the [ CII ] line ( 158 \mu m ) , we calculate a total mass of about 12 M _ { \odot } for the circumstellar envelope , but the line is likely affected by interstellar contamination .

Conclusions :