Interstellar Polarization from CO and XCN Mantled Grains: A Severe Test for Grain Alignment Mechanisms
A. Chrysostomou, J. H. Hough, D. C. B. Whittet, D. K. Aitken, P. F. Roche, A. Lazarian;
ApJ, 1996, 465, L61
ABSTRACT:We present linear spectropolarimetry in the wavelength range 4.5--4.8 mu m of the embedded infrared source W33A.
Our observations show for
the first time the presence of polarization associated with the CO and XCN
ice features, demonstrating that the absorbers reside in or on aligned
grains.
Both narrow and broad components of the solid CO feature near 4.67 mu m are
polarized.
The detection of polarization associated with the narrow CO component is
particularly significant, as the ices responsible are thought to exist only in
dense, cold regions of molecular clouds, where gas and grain temperatures are
expected to be closely coupled and traditional grain alignment mechanisms
should become ineffective.
We discuss the significance of this result with
regard to current grain alignment theories.
Mechanisms in which grain
rotational energy is enhanced by interaction with cosmic rays merit further
investigation.
KEYWORDS: ism: dust, extinction, polarization, ism: magnetic fields
PERSOKEY:polarisation, nir, dust, extinction, molecular clouds, ,
CODE: chrysostomou96