THE STRUCTURE OF THE IC-1396 REGION

We have made an extensive study of the molecular clouds associated wit h the H II region IC 1396 in the rotational transitions J=1-0 and J=2- 1 of (CO)-C-12 and (CO)-C-13 and J=3-2 of (CO)-C-12 with an average sp atial resolution of 2.5' and an average sampling of about 2.0', in ord er to get information on its structure and evolution. On the basis of our observations, which cover an area of more than 6 deg(2), we can cl assify the molecular clouds into those directly associated with the io nizing 06.5V star HD 206267, producing the bright-rimmed clouds, and t he cold gas along the line of sight, which is mainly foreground materi al. The bright-rimmed clouds show the presence of warmer molecular gas through higher (CO)-C-12(2-1)/(1-0), (CO)-C-13 (2-1)/(1-0) and (CO)-C -12 (3-2)/(2-1) line ratios than the cold foreground gas. The warm clo uds form roughly a shell-like arrangement with a diameter of 25 to 40 pc around IID 206267 (though most are slightly closer to the Sun than the O star), and they seem to be the remainder of the now dispersing m olecular cloud which gave birth to the O6.5 star and the star cluster Tr 37 associated with it. All bright-rimmed clouds show internal struc ture on all size scales, including bipolar outflows. Optical, FIR (IRA S 12 to 100 mu m) and CO maps are in close agreement over the whole re gion, especially for the bright-rimmed clouds: Exceptions are some opt ically bright (ionized) regions, which show FIR, but no CO emission, a nd the cold foreground clouds, which are very weak at FIR wavelengths. The entire mass of the mapped IC 1396 region is estimated to be 12 00 0 M., which is composed of molecular (4000 M.), atomic (5000 M.), and ionized material (3000 M.) in nearly equal amounts. The masses of the bright-rimmed clouds range from a few to several 100 M..