Age and mass studies for young star clusters in M31 from SEDs-fit
  In this paper, we present photometry for young star clusters in M31, which
are selected from Caldwell et al. These star clusters have been observed as
part of the Beijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey
from 1995 February to 2008 March. The BATC images including these star clusters
are taken with 15 intermediate-band filters covering 3000--10000 \AA. Combined
with photometry in the {\sl GALEX} far- and near-ultraviolet, broad-band
$UBVRI$, SDSS $ugriz$, and infrared $JHK_{\rm s}$ of Two Micron All Sky Survey,
we obtain their accurate spectral energy distributions (SEDs) from 1538-20000
\AA. We derive these star clusters' ages and masses by comparing their SEDs
with stellar population synthesis models. Our results are in good agreement
with previous determinations. The mean value of age and mass of young clusters
($<2$ Gyr) is about 385 Myr and $2\times 10^4 {M_\odot}$, respectively. There
are two distinct peaks in the age distribution, a highest peak at age $\sim$ 60
Myr and a secondary peak around 250 Myr, while the mass distribution shows a
single peak around $10^4 {M_\odot}$. A few young star clusters have two-body
relaxation times greater than their ages, indicating that those clusters have
not been well dynamically relaxed and therefore have not established the
thermal equilibrium. There are several regions showing aggregations of young
star clusters around the 10 kpc ring and the outer ring, indicating that the
distribution of the young star clusters is well correlated with M31's
star-forming regions. The young massive star clusters (age $\leq 100$ Myr and
mass $\geq 10^4 {M_\odot}$) show apparent concentration around the ring
splitting region, suggesting a recent passage of a satellite galaxy (M32)
through M31 disk.
