We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope ( UKIRT ) , of the Local Group spiral galaxy M 33 ( Triangulum ) .
The main aim was to identify stars in the very final stage of their evolution , and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity .
In this third paper of the series , we measure the dust production and rates of mass loss by the pulsating Asymptotic Giant Branch ( AGB ) stars and red supergiants .
To this aim , we combined our time-averaged near-IR photometry with the multi-epoch mid-IR photometry obtained with the Spitzer Space Telescope .
The mass-loss rates are seen to increase with increasing strength of pulsation and with increasing bolometric luminosity .
Low-mass stars lose most of their mass through stellar winds , but even super-AGB stars and red supergiants lose \sim 40 % of their mass via a dusty stellar wind .
More than three-quarters of the dust return is oxygenous .
We construct a 2-D map of the mass-return rate , showing a radial decline but also local enhancements due to agglomerations of massive stars .
We estimate a total mass-loss rate of 0.004–0.005 M _ { \odot } yr ^ { -1 } kpc ^ { -2 } , increasing to \sim 0.006 M _ { \odot } yr ^ { -1 } kpc ^ { -2 } when accounting for eruptive mass loss ( e.g. , supernovæ ) ; comparing this to the current star formation rate of \sim 0.03 M _ { \odot } yr ^ { -1 } kpc ^ { -2 } we conclude that star formation in the central region of M 33 can only be sustained if gas is accreted from further out in the disc or from circum-galactic regions .