Gas and dust budget of the Large Magellanic Cloud
  Recent observations from the Spitzer Space Telescope enable us to study the
mid-infrared dust excess of Asymptotic giant branch (AGB) stars in the Large
Magellanic Cloud (LMC). Using mid-infrared spectra, together with photometric
data from the SAGE programme, we establish a colour selection of carbon-rich
AGB stars with intermediate and high mass-loss rates. We also established
mass-loss rate versus colour relations for carbon-rich AGB stars. The
integrated mass-loss rate over all intermediate and high mass-loss rate
carbon-rich AGB candidates in the LMC is 8.5x10^-3 solar mass per year. This
number could be almost doubled if oxygen-rich stars are included. Gas mass-loss
rate from these stars is 4-5x10^-4 solar mass per year per kpc2 in the bar
and1x10^-4 solar mass per year per kpc^2 outside of the bar. AGB stars are one
of the most important dust sources in the LMC, and the dominant gas source
outside of the bar. As a consequence of recent increases in the star-formation
rate, supernovae are the most important gas source in the LMC bar and around 30
Dor. These differences in dust and gas sources impact on the gas-to-dust ratio
and dust properties of the local ISM, because the injection from SNe could have
a higher gas-to-dust ratio, resulting in a higher gas-to-dust ratio for the ISM
in certain regions of the LMC.
