Spectropolarimetry of the 3-micron ice band in Elias 16 (Taurus Dark Cloud)

Abstract

Polarization data between 1.2 and 3.8 μm, including spectropolarimetry in the 3-μm ice feature, are presented for the highly reddened field star Elias 16 in the Taurus Dark Cloud. The polarization is observed to increase with optical depth in the ice feature in a manner similar to that found for the BN object, that is, consistent with dichroic absorption by aligned grains. The polarization feature can be well modelled assuming grains composed of ammonia-water ices, with the ratio of H2O:NH3 greater than 3:1. The continuum polarization can be well fitted over most of the observed wavelength range assuming a mix of silicate and graphite grains with size ≡0.13 μm.