Temperature Structure of the Pipe Nebula Studied by the Intensity
  Anomaly of the OH 18 cm
  We present observations of the four hyperfine structure components of the OH
18 cm transition (1612, 1665, 1667 and 1720 MHz) toward a filamentary dark
cloud, the Pipe nebula, with the Green Bank Telescope. A statistical
equilibrium analysis is applied to the spectra,and the kinetic temperature of a
diffuse molecular gas surrounding dense cores is determined accurately; the
derived temperature ranges from 40 K to 75 K. From this result, we assess the
heating effect on the filamentarystructure of the nebula's "stem" region due to
UV photons from a nearby star $\theta$-Ophiuchi and a possible
filament-filament collision in the interface of the "stem" and "bowl" regions.
In the stem region, the gas kinetic temperature is found to be almost
independent of the apparent distance from $\theta$-Ophiuchi: the UV-heating
effect by the star is not visible. On the other hand, the gas kinetic
temperature is raised, as high as $\sim$75 K, at the interface of the two
filamentary structures. This result provides us with an additional support to
the filament-filament collision scenario in the Pipe nebula.
