The dense cloud associated with W40, one of the nearby H II regions, has been studied in millimeter-wave molecular lines and in 1.2 mm continuum. Besides, 1280 MHz and 610 MHz interferometric observations have been done. The cloud has complex morphol
ogical and kinematical structure, including a clumpy dust ring and an extended dense core. The ring is probably formed by the collect and collapse process due to the expansion of neighboring H II region. Nine dust clumps in the ring have been deconvolved. Their sizes, masses and peak hydrogen column densities are: $sim 0.02-0.11$ pc, $sim 0.4-8.1 M_{odot}$ and $sim (2.5-11)times 10^{22}$ cm$^{-2}$, respectively. Molecular lines are observed at two different velocities and have different spatial distributions implying strong chemical differentiation over the region. The CS abundance is enhanced towards the eastern dust clump 2, while the NH$_3$, N$_2$H$^+$, and H$^{13}$CO$^+$ abundances are enhanced towards the western clumps. HCN and HCO$^+$ do not correlate with the dust probably tracing the surrounding gas. Number densities derived towards selected positions are: $sim (0.3-3.2)times 10^6$ cm$^{-3}$. Two western clumps have kinetic temperatures 21 K and 16 K and are close to virial equilibrium. The eastern clumps 2 and 3 are more massive, have higher extent of turbulence and are probably more evolved than the western ones. They show asymmetric CS(2--1) line profiles due to infalling motions which is confirmed by model calculations. An interaction between ionized and neutral material is taking place in the vicinity of the eastern branch of the ring and probably trigger star formation.
Observations of distinct positions in Orion and W3 revealed ripples on the HCN(1-0), HCO^+(1-0) and CO(1-0) line profiles which can be result of emission of large number of unresolved thermal clumps in the beam that move with random velocities. The t
otal number of such clumps are ~(0.4-4) 10^5 for the areas with linear sizes ~0.1-0.5 pc.
We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high signal-to-noise ratios toward distinct positions in three selected objects in order to search for small-scale structure in molecular cloud cores associated with regions of high-ma
ss star formation. In some cases, ripples were detected in the line profiles, which could be due to the presence of a large number of unresolved small clumps in the telescope beam. The number of clumps for regions with linear scales of ~0.2-0.5 pc is determined using an analytical model and detailed calculations for a clumpy cloud model; this number varies in the range: ~2 10^4-3 10^5, depending on the source. The clump densities range from ~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal energy of the gas in the model clumps is much higher than their gravitational energy. Their mean lifetimes can depend on the inter-clump collisional rates, and vary in the range ~10^4-10^5 yr. These structures are probably connected with density fluctuations due to turbulence in high-mass star-forming regions.
