High-resolution interstellar spectroscopy and star formation

During the past several years, high spatial and spectral resolution molecular spectroscopy has greatly contributed to the knowledge of the physics, dynamics and chemistry of interstellar molecular clouds and thus has led to a better understanding of the conditions that lead to star formation. According to their physical properties, molecular clouds can be grouped into four different types: (i) the dark clouds, (ii) the molecular clouds associated with H+ regions, (iii) the 'protostellar' (or maser) environment, and (iv) the molecular envelopes of late-type stars. The first three types of cloud contain generally active regions of star formation. As typical examples the properties are discussed of individual clouds such as TMC 1 and L 183 for the cold clouds, S 140 and S 106 for the warm dark clouds with embedded infrared source, and Orion A for a region with associated H+ region. In S 140, NH3 is clumped on a scale of not more than 20'', whereas recent observations towards Orion A with the Very Large Array show that NH3 clumps on a scale smaller than 5''. (author)