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D. Li, P. F. Goldsmith (NAIC, Cornell University)
Dense cores in molecular clouds have been recognized as likely sites of future star formation. Usually identified using tracers having high critical densities, these cores possess masses between that of a single star and of a stellar cluster. According to their mass, they can be divided into two categories, low--mass cores (\lesssim 10 M\odot) found in regions such as Taurus and high--mass cores (\geq 50M\odot) typically found in GMCs. The dichotomy of cores implies the link of core initial conditions to the formation of high mass stars and O-B clusters, which are very rare in a region like Taurus or Ophiuchus.
Compared to the large volume of existing data of low--mass cores, the high--mass cores have received much less attention, partly due to the greater distances of GMCs. Our motivation for this project is to obtain an angularly--resolved data set, which will provide relatively complete initial conditions of quiescent cores in the Orion molecular cloud.
The following tracers have been chosen to obtain specific information as accurately as possible for the general conditions of GMC cores: NH3 1-0 inversion lines for kinetic temperature, 13CO and C18O 1-0 for column density, combined sets of C18O 2-1/1-0 and CS 5-4/2-1 for volume density, N2H+ for the denser component in case of heavy depletion of carbon bounded molecules, and finally, 350\mum continuum emission for the dust component and an independent estimate of the core mass.
The data accumulated so far indicate that the massive cores in Orion are cold (13K ~ 19K) and gravitationally bound (core mass up to 4 times of the virial mass). This is similar to low--mass cores except that the linewidth is generally wider and is clearly supersonic for all tracers. Further efforts will be focused on the core structures and kinematics.
The author(s) of this abstract have provided an email address for comments about the abstract: dl42@cornell.edu