“School of Astronomy”
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| Paper IPM / Astronomy / 14346 |
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We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT),
of the Local Group galaxy M33. 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. The pulsating giant stars (AGB and red
supergiants) are identified and their distributions are used to derive the star formation rate as a function
of age. These stars are also important dust factories; we measure their dust production rates from a
combination of our data with Spitzer Space Telescope mid-IR photometry. 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 superginats lose
�?�40% of their mass via a dusty stellar wind. 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. By comparing the
current star formation rate with total mass input to the ISM, we conclude that the star formation in
the central regions of M33 can only be sustained if gas is accreted from further out in the disc or from
circum-galactic regions.
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