Yonsei Evolutionary Population Synthesis (YEPS) Model. III. Surface
  Brightness Fluctuation of Normal and Helium-enhanced Simple Stellar
  Populations
  We present an evolutionary population synthesis model of the surface
brightness fluctuation (SBF) for normal and He-enriched simple stellar
populations (SSPs). While our SBF model for the normal-He population agrees
with other existing models, the He-rich population, containing hotter
horizontal-branch stars and brighter red-clump stars than the normal-He
population, entails a substantial change in the SBF of SSPs. We show that the
SBF magnitudes are affected by He-rich populations at least $\sim$0.3~mag even
in $I$- and near-IR bands at given colors, from which the SBF-based distances
are often derived. Due to uncertainties both in observations and models,
however, the SBFs of Galactic globular clusters and early-type galaxies do not
allow verifying the He-enriched model. We propose that when combined with
independent metallicity and age indicators such as ${\rm Mg}_2$ and ${\rm
H}\beta$, the UV and optical SBFs can readily detect underlying He-rich
populations in unresolved stellar systems at a distance out to $\gtrsim
20$\,Mpc. A full set of the spectro-photometric and SBF data for SSPs from the
Yonsei Evolutionary Population Synthesis (YEPS) model is available for download
at http://cosmic.yonsei.ac.kr/YEPS.htm.
