A schematic view of the complex interaction between star formation and evolution and the interstellar medium is given in the figure below. Changes in the abundances of different molecules during core formation and collapse, which can be measured with high-resolution spectroscopy, are expected to provide critical information for understanding the star formation process. These surveys will allow us to search for dense cold clumps as small as 0.03 Msun and will allow us to obtain reliable estimates of the lifetimes of the isothermal and the dense embedded phase of protostellar collapse. It is these earliest phases in the formation of a star which provide the strongest constraint on theoretical models of star formation. The star formation process is accompanied by an evolution in chemical complexity.
Water plays a crucial role in both the physics and the chemistry of star forming regions.
Water is one of the major reservoirs of oxygen, as well as one of the main coolants of star forming clouds. The relative intensities of different far-infrared water lines provide powerful diagnostics of the density, temperature, and thermal radiation from dust in star forming regions. This heterodyne instrument uses pairs of double sideband SIS mixers in dual polarization for the long wavelength band, and a single hot electron bolometer for each of the short wavelength bands. Thus, at this wavelength, HIFI will be four times more sensitive than the JCMT, but will have 3.5 times worse spatial resolution. It has a field of view of 2' and is optimized for spectral surveys.