CO Observations of the tex2html_wrap_inline211-Orionis Ring

W.J. Lang , M.R.W. Masheder, PASA, 15 (1), 70
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To obtain maximum signal-to-noise in two-dimensional maps from the datacube we use the masked moment analysis technique (eg. Digel et al. 1996). Figure 1 displays a zeroth moment Wtex2html_wrap_inline253 map. The equivalent of the lowest contour in the MM map lies at the tex2html_wrap_inline2553 K km stex2html_wrap_inline245 level in the new map. The much greater depth of the new survey results from a combination its intrinsically better sensitivity-per-unit-area and from the data analysis techniques utilised. The newly discovered emission accounts for approximately three-quarters of the total area of emission, yet contributes only tex2html_wrap_inline259 30% of the total integrated emission.

The map shows the Ring roughly subdivides into three main components: B223 to the south, B30 to the west, and an extended complex of low-level emission containing the clouds B35 and L1598/1599 to the northeast. These denser areas are the remains of density enhancements in the original GMC rather than material swept up by the expansion of the HII region.

Figure 1: Zeroth moment map of velocity-integrated emission, Wtex2html_wrap_inline253. Contours are at 0.3, 0.6, 1.2, 2.4.....etc K km stex2html_wrap_inline245. Emission covers the velocity range [-10,+20] km stex2html_wrap_inline245 with respect to the LSR.

Velocity Structure

Figure 2 shows that the Ring is split into two dominant velocity components. The southern complex lies around -2 km stex2html_wrap_inline245, while the other strong emission is at around 8 km stex2html_wrap_inline245. It is difficult to determine if weak emission spatially links the two, as we might expect from a continuous shell or ring structure. It seems unlikely that such a definite bifurcation in velocity could result entirely from the expansion of the HII region. More credible is the idea that we are dealing with the disruption of what was initially two distinct cloud complexes, with different initial velocities. Indeed, the southern part of the Ring appears spatially and kinematically connected to Barnard's Loop and its associated HI features (Zhang and Green 1991).

Figure 2: Velocity-position moment maps, (v,l) and (v,b). Contours are 0.12, 0.24, 0.48, 0.96.....etc K degrees.


The datacube was subdivided into individual emission features (`clumps') , using the CLUMPFIND algorithm (Williams et al. 1994). We found 130 distinct clumps. The clump parameters are available in tabulated form that can be obtained via email from the authors.

Next Section: Interpretation
Title/Abstract Page: CO Observations of the
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Contents Page: Volume 15, Number 1

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