Paper: astro-ph/0601077
Date: Wed, 4 Jan 2006 19:22:27 GMT (361kb)

Title: Hubble Space Telescope NICMOS Polarization Measurements of OMC-1

Authors: Janet P. Simpson (1 and 2), Sean W. J. Colgan (1), Edwin F. Erickson
(1), Michael G. Burton (3), and A. S. B. Schultz (2) ((1) NASA Ames Research
Center, (2) SETI Institute, (3) University of New South Wales)

Comments: 41 pages, 8 figures, 4 tables, to appear in The Astrophysical Journal
\\
We present 2micron polarization measurements of positions in the BN region of
the Orion Molecular Cloud (OMC-1) made with NICMOS Camera 2 (0.2'' resolution)
on HST. Our results are as follows: BN is sim 29% polarized by dichroic
absorption and appears to be the illuminating source for most of the nebulosity
to its north and up to sim 5'' to its south. Although the stars are probably
all polarized by dichroic absorption, there are a number of compact, but
non-point-source, objects that could be polarized by a combination of both
dichroic absorption and local scattering of star light. We identify several
candidate YSOs, including an approximately edge-on bipolar YSO 8.7'' east of
BN, and a deeply-embedded variable star. Additional strongly polarized sources
are IRc2-B, IRc2-D, and IRc7, all of which are obviously self-luminous at
mid-infrared wavelengths and may be YSOs. None of these is a reflection nebula
illuminated by a star located near radio source I, as was previously suggested.
Other IRc sources are clearly reflection nebulae: IRc3 appears to be
illuminated by IRc2-B or a combination of the IRc2 sources, and IRc4 and IRc5
appear to be illuminated by an unseen star in the vicinity of radio source I,
or by Star n or IRc2-A. Trends in the magnetic field direction are inferred
from the polarization of the 26 stars that are bright enough to be seen as
NICMOS point sources. The most polarized star has a polarization position angle
different from its neighbors by sim 40^o, but in agreement with the grain
alignment inferred from millimeter polarization measurements of the cold dust
cloud in the southern part of OMC-1.

\\ ( http://arXiv.org/abs/astro-ph/0601077 , 361kb)