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Session 17 - Molecular Clouds and Star Formation.
Oral session, Monday, June 10
Humanities 2650,

[17.05] BIMA 13CO and C18O Observations of W3

D. A. Roberts (NCSA), R. M. Crutcher (U. Illinois), T. H. Troland (U. Kentucky)

The W3 molecular cloud core has been observed with the BIMA and NRAO 12 m telescopes in the ^13CO (J = 1--0) and (J = 1--0) lines. Two BIMA fields were imaged, centered on the two infrared sources IRS 5 and IRS 4 (80^\prime\prime west of IRS 5).

The total masses of the the molecular cores associated with IRS 4 and IRS 5 are 1700 and 1100 M_ødot, respectively. Seven clumps between 0.11 and 0.33 pc in size are identified with H_2 column densities in the range 1.3 to 2.1 \times 10^23 cm^-2. Derived masses are between 120 and 480 M_ødot; under simple geometrical assumptions, n(H_2) is between 1.8 to 4.5 \times 10^5 cm^-3. For both cores the sum of all the individual clumps was about half of the total mass. The virial masses of the clumps ranged from 80 to 660 M_ødot. The virial masses are near the measured H_2 masses. Comparisons of the ^13CO and C^18O line strengths provide an estimate of the optical depth in ^13CO, assuming the C^18O line has a negligible opacity. For two clumps located at IRS 5 and 20^\prime\primesouth of IRS 4 an opacities derived were 0.3 and 0.7, respectively. At the positions of IRS 4 and IRS 5, clumps are observed; the IRS 4 clump in particular has a n(H_2) about a factor of two larger than the other clumps.

At the position of IRS 5, the data show a systematic velocity structure suggestive of rotation. A Keplarian velocity field was fitted to the data, which yielded a dynamical mass of 100 M_ødot. Integrating the emission from the same clump over the same velocity range gives a H_2 masss of 110 M_ødot. Using the derived H_2 column density toward IRS 5 and a previous HI Zeeman result, we can derive the ratio |B|/N_H (which is proportional to the magnetic flux-to-mass ratio, \Phi/H_H) can be derived. The determined ratio is near the magnetically critical value, which is consistent with the standard theory of high mass star formation.

Program listing for Monday