W 49 A North: J=2-1 Lines of CS and C(18) O

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Observations of the W 49 A North star forming region in the J=2-1 line of CS have been made with the BIMA array with an angular resolution of 4.6'' x 3.8''; complementary observations in the J=2-1 line of C(18) O and J=3-2 line of C(34) S were made with the IRAM 30 meter telescope with angular resolutions of 12'' and 17'' respectively. The molecular complex is elongated along a diagonal from northeast to southwest. The position-velocity diagrams for CS convolved to 12'' resemble those of C(18) O and the J=5-4 line of C(34) S (from Serabyn et al. 1993). There is a change in velocity along the major axis of the molecular complex. At the higher resolution of ~ 4'', absorption of the continuum emission at 3 mm by CS is clearly observed. The apparent velocity gradient is seen to be part of a``C''-shaped distribution of the CS emission. Furthermore, as is found in the J=1-0 HCO(+) data by Welch et al. (1987), the optically thick J=2-1 CS line exhibits an inverse P-Cygni profile towards HII region G. These two characteristics of the CS data lend support to the global collapse model (Welch et al. 1987). The high resolution CS profiles in the central region all show varying degrees of absorption. At lower resolution the surrounding CS emission fills in much of the absorption and the inverse P-Cygni shape disappears. Most spectra towards W 49 A North show two main velocity components whose relative intensities vary with position along the major axis of the molecular complex. It is not clear whether this behavior can also be explained using the global collapse model of Welch et al. together with self-absorption effects; it may be necessary to include some additional cloud components as proposed by Serabyn et al. (1993). Radiative transfer modeling of these and other scenarios is nearing completion and is the subject of a separate paper (Williams and Dickel, in preparation 1999). Research was partially supported by NSF grants to UIL and UCB.

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