The Ages of M31 Star Clusters: Spectral Energy Distribution Versus
  Color-Magnitude Diagram
  It is well-known that fitting the Color Magnitude Diagrams (CMDs) to the
theoretical isochrones is the main method to determine star cluster ages.
However, when the CMDs are not available, the Spectral Energy Distribution
(SED)-fitting technique is the only other approach, although it suffers the
age-metallicity-reddening degeneracy. In this work, we gather the ages,
metallicities and masses of dozens of M31 star clusters from the CMD-fitting
with HST images from the literatures for comparison. We check the reliability
of the SED-fitting results with different models, i.e., Bruzual \& Charlot 2003
model (BC03), Galaxy Evolutionary Synthesis Models ({\sl GALEV}) and Advanced
Stellar Population Synthesis (ASPS) for the simple stellar populations (SSPs)
with single stars (ss)-SSP/binary star (bs)-SSPs models. The photometry bands
includes the Galaxy Evolution Explorer {\sl GALEX} FUV/NUV bands,
optical/near-infrared $UBVRIJHK$ bands, as well as the Wide-field Infrared
Survey Explorer ({\sl WISE}) $W1$/$W2$ bands. The comparisons show that the
SED-fitting ages agree well with the CMD-fitting ages, either with the fixed
metallicity or with the free metallicity for both the BC03 and the {\sl GALEV}
model. However, for the ASPS models, it seems that SED-fitting results are
systematic older than the CMD ages, especially for the ages log t <9.0 (yr).
The fitting also shows that the {\sl GALEX} FUV/NUV-band are more important
than the {\sl WISE} $W1$/$W2$ for constraining the ages, which confirms the
previous findings. We also derived the masses of our sample star clusters from
the BC03 and {\sl GALEV} models and it is found that the values agree well with
that in the literature.
