Tracers of Stellar Mass-loss - II. Mid-IR Colors and Surface Brightness
  Fluctuations
  I present integrated colors and surface brightness fluctuation magnitudes in
the mid-IR, derived from stellar population synthesis models that include the
effects of the dusty envelopes around thermally pulsing asymptotic giant branch
(TP-AGB) stars. The models are based on the Bruzual & Charlot CB* isochrones;
they are single-burst, range in age from a few Myr to 14 Gyr, and comprise
metallicities between $Z$= 0.0001 and $Z$ = 0.04. I compare these models to
mid-IR data of AGB stars and star clusters in the Magellanic Clouds, and study
the effects of varying self-consistently the mass-loss rate, the stellar
parameters, and the output spectra of the stars plus their dusty envelopes. I
find that models with a higher than fiducial mass-loss rate are needed to fit
the mid-IR colors of "extreme" single AGB stars in the Large Magellanic Cloud.
Surface brightness fluctuation magnitudes are quite sensitive to metallicity
for 4.5 um and longer wavelengths at all stellar population ages, and powerful
diagnostics of mass-loss rate in the TP-AGB for intermediate-age populations,
between 100 Myr and 2-3 Gyr.
