Prof Patrick Roche

Abstract:

We present spectropolarimetry of the 3.1 μm water-ice feature in the Becklin-Neugebauer (BN) object in OMC-1, with spectral resolution and signal-to-noise ratios substantially improved over previous observations. The well-known increase in polarization within the ice feature is interpreted in terms of a model for aligned graphite and silicate grains with ice mantles. We identify polarization structure in the long-wavelength (3.3-3.6 μm) wing of the ice profile, including a feature at 3.47 μm which matches closely the spectroscopic feature discovered in several protostars and attributed to carbonaceous material with diamond-like structure. We also show, for the first time, the occurrence of a systematic variation in the position angle of polarization across the ice feature in BN, indicating systematic differences in the relative numbers of core-mantle and unmantled grains along the line of sight, and a twist in the magnetic field orientation. © 1996. The American Astronomical Society. All rights reserved.

Abstract:

Spectra at 5-5.6 μm are presented of three planetary nebulae with strong unidentified infrared (UIR) emission bands. All three objects display the 5.25-μm emission band which is attributed to a combination band arising from out-of-plane C-H bending modes. The profiles of the 5.25-μm bands are closely similar to those of the 3.4- and 11.25-μm emission features, confirming that the 5.25-μm feature is a member of the UIR-band family. The origin of this band and its relationship to the UIR bands in the 3.4-3.6 and 11-13 μm spectral regions are discussed. An interpretation of these features in terms of combinations and overtones of the C-H out-of-plane modes is suggested, which, if correct, leads to a simplification of the UIR-band spectrum and suggests that the species that give rise to the bands must have a high degree of symmetry.