Spectropolarimetry of the 3-micron ice feature in molecular clouds. II : GL 2591, GL 2136, W 33A and Elias 29 (Rho Ophiuchi dark cloud)

Abstract

Spectropolarimetric observations in the 3-micron ice band are presented for the infrared sources GL 2591, GL 2136, W 33A and Elias 29 (Rho Ophiuchi dark cloud). Some continuum polarization measurements between 1.2 and 5.0 microns are also considered. Increasing polarization with optical depth within the ice feature are observed for GL 2136 and Elias 29 confirming that there is little or no increase in the level of polarization within the same feature for GL 2591, in contrast with the polarization increases that have previously been observed for this source across the 10- and 20-micron silicate features. For W 33A, observations were possible only in the wing of the ice feature, in which there is no significant increase in polarization with optical depth. Possible explanations for the lack of enhanced polarization across the 3-micron ice feature of GL 2591 (and possibly W 33A) are presented.