  This article presents a multi-wavelength study towards S87, based on a
dataset of submillimeter/far-/mid-infrared (sub-mm/FIR/MIR) images and
molecular line maps. The sub-mm continuum emission measured with JCMT/SCUBA
reveals three individual clumps, namely, SMM1, SMM2, and SMM3. The MIR/FIR
images obtained by the Spitzer Space Telescope indicate that both SMM1 and SMM3
harbor point sources. The J=1-0 transitions of CO, 13CO, C18O, and HCO+,
measured with the 13.7m telescope of the Purple Mountain Observatory, exhibit
asymmetric line profiles. Our analysis of spectral energy distributions (SEDs)
shows that all of the three sub-mm clumps are massive (110--210 $M_{\odot}$),
with average dust temperatures in the range ~20--40K. A multi-wavelength
comparison convinces us that the asymmetric profiles of molecular lines should
result from two clouds at slightly different velocities, and it further
confirms that the star-forming activity in SMM1 is stimulated by a cloud-cloud
collision. The stellar contents and SEDs suggest that SMM1 and SMM3 are
high-mass and intermediate-mass star-forming sites respectively. However, SMM2
has no counterpart downwards 70 micron, which is likely to be a cold high-mass
starless core. These results, as mentioned above, expose multiple phases of
star formation in S87.
