Far-Infrared Spectroscopic Survey of Near-by Interstellar Clouds

The far-infrared [C II] spectral line (^2P_-^2P_,157.7409 mum), which is emitted by singly ionized carbon (C^+), is the dominant coolant of neutral interstellar clouds. Hence observations of the line is crucial to reveal the physical states, especially the energy budget, of interstellar clouds. We have been successfully making survey observations of the [C II] line using a dedicated observing instrument BICE.The observational results are very important for interstellar physics. However, since there are various components in a line sight toward the Galactic plane, the observational results are rather complicated. Hence the [C II] observations of indivudual clouds which have a single component in a line sight are very important to understand the physical properties of the [C II] emitting regions. To make templates of [C II] emitting regions, we observed the Orion regions, which is the most representative massive-star-forming regions. The observation was carried out on September 3,1994, from the Sanriku Balloon Center, using the BICE. The observation revelaed that there are several groups of [C II] emitting regions with different physical parameters in the Orion regions. Using the results, we reinvestigated our previous [C II] observations of the Galactic plane.