The Mass-Loss Return From Evolved Stars to the LMC: Empirical Relations
  for Excess Emission at 8 and 24 \mu m
  We present empirical relations describing excess emission from evolved stars
in the Large Magellanic Cloud (LMC) using data from the SAGE (Surveying the
Agents of a Galaxy's Evolution) survey which includes the IRAC 3.6, 4.5, 5.8
and 8.0 \mu m and MIPS 24, 70 and 160 \mu m bands. We combine the SAGE data
with the Two Micron All Sky Survey (2MASS; J, H and Ks) and the optical
Magellanic Cloud Photometric Survey (MCPS; U, B, V and I) point source catalogs
to create complete spectral energy distributions (SEDs) of the asymptotic giant
branch (AGB) star candidates in the LMC. AGB star outflows are among the main
producers of dust in a galaxy, and this mass loss results in an excess in the
fluxes observed in the 8 and 24 \mic m bands. We identify oxygen-rich,
carbon-rich and extreme AGB star populations in our sample based on their 2MASS
and IRAC colors. We calculate excesses fluxes in the mid-IR bands by comparison
of the SEDs with model photospheres. We find about 16,000 O-rich, 6300 C-rich
and 1000 extreme sources with reliable 8 \mu m excesses, and about 4500 O-rich,
5300 C-rich and 960 extreme sources with reliable 24 \mic m excesses. The
excesses are in the range 0.1 mJy--5 Jy. The 8 and 24 \mic m excesses for all
three types of AGB candidates show a general increasing trend with luminosity.
The dust color temperature derived from the ratio of the 8 and 24 \mic m
excesses decreases with an increase in excess, while the 24 \mic m optical
depth increases with excess. The extreme AGB candidates are the major
contributors to the mass loss, and we estimate the total AGB mass-loss return
to the LMC to be (5.9--13)\times 10^{-3} Msun yr^{-1}.
