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Title:
Hubble Space Telescope NICMOS Polarization Measurements of OMC-1
Authors:
Simpson, Janet P.; Colgan, Sean W. J.; Erickson, Edwin F.; Burton, Michael G.; Schultz, A. S. B.
Affiliation:
AA(NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000 , , ; Also at the SETI Institute, 515 North Whisman Road, Mountain View, CA 94043.), AB(NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000 , , ), AC(NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000 , , ), AD(School of Physics, University of New South Wales, Kensington, Sydney, NSW 2052, Australia; ), AE(SETI Institute, 515 North Whisman Road, Mountain View, CA 94043; )
Publication:
The Astrophysical Journal, Volume 642, Issue 1, pp. 339-353. (ApJ Homepage)
Publication Date:
05/2006
Origin:
UCP
ApJ Keywords:
Infrared: ISM, Infrared: Stars, ISM: individual (Orion BN/KL), ISM: Magnetic Fields, Stars: Formation, Stars: Pre-Main-Sequence
DOI:
10.1086/500656
Bibliographic Code:
2006ApJ...642..339S

Abstract

We present 2 μm polarization measurements of positions in the IRc2 and BN regions of the Orion Molecular Cloud (OMC-1) made with NICMOS Camera 2 (0.2" resolution) on the Hubble Space Telescope. Our results are as follows: BN is ~29% polarized by dichroic absorption and appears to be the illuminating source for most of the nebulosity to its north and for up to ~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 starlight. 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 ~40°, but in agreement with the grain alignment inferred from millimeter polarization measurements of the cold dust cloud in the southern part of OMC-1.
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