The Mass-Loss Return From Asymptotic Giant Branch Stars to The Large
  Magellanic Cloud Using Data From The SAGE Survey
  The asymptotic giant branch (AGB) phase is the penultimate stage of evolution
for low- and intermediate-mass stars. AGB star outflows inject a significant
amount of material into the interstellar medium (ISM), seeding new star
formation. AGB mass loss is thus a crucial component of galactic chemical
evolution. The Large Magellanic Cloud (LMC) is an excellent site for AGB
studies. Over 40,000 AGB candidates have been identified using photometric data
from the Spitzer Space Telescope Surveying The Agents of a Galaxy's Evolution
(SAGE) mid-infrared (MIR) survey, including about 35,000 oxygen-rich, 7000
carbon-rich and 1400 "extreme" sources. For the first time, SAGE photometry
reveals two distinct populations of O-rich sources in the LMC: a faint
population that gradually evolves into C-rich stars and a bright, massive
population that circumvents this evolution, remaining O-rich. This work aims to
quantify the mass-loss return from AGB stars to the LMC, a rough estimate for
which is derived from the amount of MIR dust emission in excess of that from
starlight. I show that this excess flux is a good proxy for the mass-loss rate,
and I calculate the total AGB injection rate to be (5.9-13) x 10{-3} Msun/yr. A
more accurate determination requires detailed dust radiative transfer (RT)
modeling. For this purpose, I present a grid of C-rich AGB models generated by
the RT code 2DUST, spanning a range of effective temperatures, gravities, dust
shell radii and optical depths as well as a baseline set of dust properties
obtained by modeling a carbon star, data for which was acquired as part of the
spectroscopic follow-up to SAGE. AGB stars are the best laboratories for dust
studies, and the development of a model grid will reinforce future research in
this field.
