Molecular line and continuum study of the W40 cloud
  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 morphological 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.
