  We made a multi-wavelength study of young massive star clusters (YSCs) in the
interacting galaxy ARP 24, using the optical and ultraviolet images from Hubble
Space Telescope (HST), Sloan Digital Sky Survey, and Galaxy Evolution Explorer;
the mid-infrared images from Spitzer Space Telescope; and the narrow-band Ha
image and optical spectra from the NAOC 2.16m telescope. Based on the HST
images, we found that the brightest infrared knot in ARP 24 is associated with
a complex of five young massive star clusters, within a region of ~ 0.95"
radius (127pc) in size. The ages and masses of the star clusters in this
complex and other regions were estimated using HST broadband photometries and
the Starburst99 synthesis models. The star clusters in this complex are very
young (within ages of ~ 3-5 Myr) and massive (masses of ~ 10^5 Msun). The
ionization parameter and metallicity of the complex were estimated using the
emission line ratios, and the star formation rates were calculated using
monochromatic 24um, FUV, and Ha line luminosities. We speculate that ARP 24 may
formed by a retrograde fly-by encounter indicated by its one-armed appearance
and fan-like structure, and the formation of the YSCs in this galaxy is
triggered by the interaction. The clusters in the YSC complex may formed in a
single giant molecular cloud simultaneously. From the ultraviolet to
mid-infrared spectral energy distributions, we found that the region of the YSC
complex is relatively bluer in optical and has higher 24um dust emission
relative to the starlight and 8um emission. This warm infrared color may due to
strong UV radiation field or other mechanisms (e.g., shocks) within this region
which may destroy the Polycyclic Aromatic Hydrocarbons and enhance the small
grain emission at 24um.
