% TEX version of NRAO Radio CD-ROM image submission form 
% Version 91/3/28    J. J. Condon

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\centerline{\bf NRAO CD-ROM IMAGE SUBMISSION FORM}

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\noindent Image Donor(s): F. Yusef-Zadeh

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\noindent Contact donor: F. Yusef-Zadeh

Mailing address: Northwestern University, Department of Physics and
Astronomy, Evanston, IL 60201

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Telephone: 708 491-8147

E-mail address: zadeh@ossenu.astro.nwu.edu

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\noindent Source or Image Name: Orion Nebula

\noindent Alternate Names: 

\noindent Description of Observation: (e.g., date of observation,
telescope(s) used, frequencies, polarization type, resolution, 
deconvolution method) 


The radio observations were carried out at 20 cm using the VLA
in its A, B, C, and D configurations in 1987 July, 1986 September,
1986 October, and 1986 January, respectively. In order to ensure the
lack of bandwidth smearing of the radio images, the frequency bandwidths
used in these observations were 3.125, 6.25, 12.5, and 25 MHz for the
A, B, C, and D arrays, respectively. The data were self-calibrated,
CLEANed with the AIPS task SDCLN, and mosaicked.  The resolution
is 1.8 arcsec by 1.6 arcsec.

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\noindent Description of Image: (e.g., type of source, scientific reason
for observing, notable source features)

The overall morphology of ionized gas at 20 cm wavelength shows a number 
of striking new substructures associated with this geometrically
complex HII region.  On the largest scale, we find a number of linear
features, which are considered as new ionization fronts, and which form
a 40^\circ angle with respect to the main ionization front known as the
``bar'' in M42.  These features together with the ridge of emission
from the optical bar form a conelike appearance whose 5--10 arcmin
envelope is centered near the Trapezium cluster.  On a small scale, we
report the detection of a web of stringlike features with typical widths
of a few arcseconds ($\approx 10^{16}$ cm) which are concentrated
throughout the Trapezium region.  These features reveal morphological
evidence for production of shocked ionized gas in star-forming 
regions, perhaps driven by powerful winds from mass-losing stars 
and/or by the shock fronts produced at the edge of expanding HII regions.

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\noindent Publication Reference(s): 

Yusef-Zadeh, F.
``Structural Details of the Orion Nebula: Detection of a Network of String-like
Ionized Features,'' 1990, {\it Ap.J.(Letters), \bf 361}, pp. L19-L22.

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\noindent Permission is granted to NRAO/AUI to use, distribute, sell, reproduce
or authorize others to use, distribute, sell or reproduce the
images listed above without reservation or restriction.  The donor
whose signature appears below agrees to inform all co-authors of this
release.

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\noindent Signed:

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\noindent Date: 5/5/92

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