Hubble Space TelescopeNICMOS Polarization Measurements of OMC‐1

We present 2micron polarization measurements of positions in the BN region ofthe 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 dichroicabsorption and appears to be the illuminating source for most of the nebulosityto its north and up to sim 5'' to its south. Although the stars are probablyall polarized by dichroic absorption, there are a number of compact, butnon-point-source, objects that could be polarized by a combination of bothdichroic absorption and local scattering of star light. We identify severalcandidate YSOs, including an approximately edge-on bipolar YSO 8.7'' east ofBN, and a deeply-embedded variable star. Additional strongly polarized sourcesare IRc2-B, IRc2-D, and IRc7, all of which are obviously self-luminous atmid-infrared wavelengths and may be YSOs. None of these is a reflection nebulailluminated by a star located near radio source I, as was previously suggested.Other IRc sources are clearly reflection nebulae: IRc3 appears to beilluminated by IRc2-B or a combination of the IRc2 sources, and IRc4 and IRc5appear 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 inferredfrom the polarization of the 26 stars that are bright enough to be seen asNICMOS point sources. The most polarized star has a polarization position angledifferent from its neighbors by sim 40^o, but in agreement with the grainalignment inferred from millimeter polarization measurements of the cold dustcloud in the southern part of OMC-1.Comment: 41 pages, 8 figures, 4 tables, to appear in The Astrophysical Journa