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We present high resolution observations of CS(J=1-0), H13CO+ (J=1-0), andSiO(v=0:J=1-0) lines, together with the 49GHz and 86GHz continuum emissions,toward W49N carried out with Nobeyama Millimeter Array. We identified 11 CS, 8H13CO+, and 6 SiO clumps with radii of 0.1-0.5pc. The CS and H13CO+ clumps aremainly divided into two velocity components, one at 4kms-1 and the other at12kms-1, while the SiO clumps have velocities between the two components. TheSiO emission is distributed toward the UCHII ring, where the 4kms-1 componentclumps of CS and H13CO+ also exist. The 12kms-1 component clumps of CS aredetected at the east and west of the UCHII ring with an apparent hole towardthe ring. The clump masses vary from 4.4x10^2 M_SUN to 4.9x10^4 M_SUN with themean values of 0.94x10^4M_SUN, 0.88x10^4M_SUN, and 2.2x10^4M_SUN for the CS,H13CO+, and SiO clumps, respectively. The total masses derived from CS, H13CO+,and SiO clumps are 1.0x10^5M_SUN, 0.70x10^5M_SUN, and 1.3x10^5 M_SUN,respectively, which agree well with the corresponding virial masses of0.71x10^5M_SUN, 1.3x10^5M_SUN, and 0.88x10^5M_SUN, respectively. The averagemolecular hydrogen densities of the clumps are 0.90x10^6 cm-3, 1.4x10^6cm-3,and 7.6x10^6 cm-3 for the CS, H13CO+ and SiO clumps, respectively. The densityderived from the SiO clumps seems significantly higher than those from theothers, probably because the SiO emission is produced in high density shockedregions. The free fall time scale of the clumps is estimated to be ~3x10^4 yr,which gives an accretion rate of 3x10-3-1M_SUN yr-1 onto a stellar core. Theobserved clumps are, if they are undergoing free fall, capable of producingdozens of massive stars in the next 10^5 yr. We propose a view thatpre-existing two clouds collided with each other almost face-on to produce theobserved clumps and triggered the burst of massive star formation in W49N.

Star burst in W49N presumably induced by cloud-cloud collision