Effects of Alpha-Element Enhancement and the Thermally
  Pulsing-Asymptotic Giant Branch on Surface Brightness Fluctuation Magnitudes
  and Broadband Colors
  We investigate the effects of alpha-element enhancement and the thermally
pulsing-asymptotic giant branch (TP-AGB) stars on the surface brightness
fluctuation (SBF) magnitudes and broadband colors of simple stellar populations
and compare to the empirical calibrations. We consider a broad range of ages
and metallicities using the recently updated Teramo BaSTI isochrones. We find
that the alpha-element enhanced I-band SBF magnitudes are about 0.35 mag
brighter and their integrated V - I colors are about 0.02 mag redder, mostly
because of oxygen enhancement effects on the upper red giant branch and
asymptotic giant branch. We also demonstrate, using both the Teramo BaSTI and
Padova isochrones, the acute sensitivity of SBF magnitudes to the presence of
TP-AGB stars, particularly in the near-IR, but in the I-band as well. Empirical
SBF trends therefore hold great promise for constraining this important but
still highly uncertain stage of stellar evolution. In a similar vein,
non-negligible disparities are found among several different models available
in the literature due to intrinsic model uncertainties.
