The W3 molecular cloud core has been observed with the BIMA and NRAO 12 m telescopes in the (13) CO (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('') west of IRS 5). The total masses of the the molecular cores associated with IRS 4 and IRS 5 are 1700 and 1100 M_sun, 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 x 10(23) cm(-2) . Derived masses are between 120 and 480 M_sun; under simple geometrical assumptions, n(H_2) is between 1.8 to 4.5 x 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_sun. The virial masses are near the measured H_2 masses. Comparisons of the (13) CO and C(18) O line strengths provide an estimate of the optical depth in (13) CO, assuming the C(18) O line has a negligible opacity. For two clumps located at IRS 5 and 20('') south 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_sun. Integrating the emission from the same clump over the same velocity range gives a H_2 masss of 110 M_sun. 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.
American Astronomical Society Meeting Abstracts #188
- Pub Date:
- May 1996