2008ApJ...680..446X

This article presents a multiwavelength study toward S87, based on a data set of submillimeter/far-infrared/mid-infrared (submillimeter/FIR/MIR) images and molecular line maps. The submillimeter continuum emission measured with JCMT SCUBA reveals three individual clumps, namely, SMM 1, SMM 2, and SMM 3. The MIR/FIR images obtained by the Spitzer Space Telescope indicate that both SMM 1 and SMM 3 harbor point sources. The J=1-0 transitions of CO, ¹³CO, C¹⁸O, and HCO⁺, measured with the 13.7 m telescope of the Purple Mountain Observatory, exhibit asymmetric line profiles. Our analysis of spectral energy distributions (SEDs) shows that all three of the submillimeter clumps are massive (110-210 M_☉), with average dust temperatures in the range ∼20-40 K. A multiwavelength 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 SMM 1 is stimulated by a cloud-cloud collision. The stellar contents and SEDs suggest that SMM 1 and SMM 3 are high-mass and intermediate-mass star-forming sites, respectively. However, SMM 2 has no counterpart below 70 µm, which is likely to be a cold high-mass starless core. These results, as mentioned above, expose multiple phases of star formation in S87.