Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996adil...dr...02r&link_type=abstract
NCSA Astronomy Digital Image Library
Astronomy and Astrophysics
Astronomy
Scientific paper
The W3 molecular cloud core has been observed with the BIMA and NRAO 12 m telescopes in the 13CO (J = 1--0) and C18O (J = 1--0) lines. Two BIMA fields were imaged, centered on the two infrared sources IRS 5 and IRS 4 (80 arcsec west of IRS 5). In order to observe large scale structure, a full-synthesis cube was made with a resolution of 9.5 times 8.0 arcsec resolution. Additionally a high-resolution cube was made with only the IRS 5 pointing of BIMA to observe the small scale distribution of gas near IRS 5. The total masses of the the molecular cores associated with IRS 4 and IRS 5 are 1700 and 1100 solar masses, respectively. Seven clumps between 0.11 and 0.33 pc in size are identified with molecular hydrogen column densities in the range 1.3 to 2.1 times 10E23 per square cm. Derived masses are between 120 and 480 solar masses and under simple geometrical assumptions, the volume density of hydrogen is between 1.8 to 4.5 times 10E5 per cubic cm. For both cores the sum of all the individual clumps was about half of the total mass; the virial masses of the clumps range from 80 to 660 solar masses. The virial masses are near the measured molecular hydrogen masses to withing 0.3. Comparisons of the 13CO and C18O line strengths provide an estimate of the optical depth in 13CO, assuming the C18O line has a negligible opacity. For the clumps located at IRS 5 and 20 arcsec south of IRS 4 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 volume density about a factor of two larger than the other clumps. At the position of IRS 5, the high-resolution 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 solar masses. Integrating the emission from the same clump over the same velocity range gives an molecular hydrogen mass of 110 solar masses. Using the derived molecular column density toward IRS 5 and a previous netural hydrogen Zeeman result, the ratio of the magnetic field to the column density (which is proportional to the magnetic flux to mass ratio). The determined ratio is near the magnetically critical value, which is consistent with the standard theory of high mass star formation.
Crutcher Richard M.
Roberts Daniel A.
Troland Thomas H.
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