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Session 10 - Interstellar Medium and Star Formation.
Display session, Monday, June 08
Atlas Ballroom,
We present HST NICMOS narrowband images of OMC-1 taken during the January, 1998 camera 3 campaign. The lines observed were P\alpha (1.87 \micron), [FeII] (1.64 \micron), and H_2 1-0 S (2.12 \micron), plus adjacent continuum filters. The images have a spatial resolution of 0.2\arcsec\ per pixel, and are centered roughly on BN. The P\alpha and H_2 observations cover an area 2\arcmin\ square; the [FeII] observations cover an area 1\arcmin\ square. These images cover a greater area than our previous study of this region (Stolovy, et al 1998 ApJ 492 L15), and include observations of P\alpha and [FeII] not done previously.
The main H_2 feature is the remarkable array of linear filamentary structures, aka ``fingers'', emanating radially from the general vicinity of BN/IRc2, and extending over much of the image. These structures are similar to those found much farther from BN/IRc2 by Allen amp; Burton (1993 Nature 363 54), generally attributed to shock emission. Some have bright bow shocks at their tips; many of the structures are quite complex, and have a ``nested'' appearance. The brightest H_2 emission in our image comes from more chaotic regions to the N and SE of BN.
The P\alpha emission generally has a wispy appearance, resembling the optical emission seen by WFPC2. The P\alpha does not coincide with the H_2 emission, and is probably excited radiatively, rather than by shocks. HH 202 is found to have P\alpha emission, and also exhibits 2 \micron\ continuum; its infrared morphology is similar to its optical morphology. We also find P\alpha emission in several previously identified proplyds.
Most of the [FeII] emission has a distribution much like P\alpha, suggesting that it too is largely radiatively excited. The [FeII] is also seen in a few clumps, e.g. in HH 208. We do not see [FeII] at the tips of most of the H_2 fingers.
