Prof Patrick Roche

Abstract:

L1551-IRS5 is a classic example of a low-mass young stellar object. We present near-infrared images with a FWHM of 0.3 arcsec obtained using the 'Shift and Add' technique. These observations are combined with existing multiwaveband data to constrain Monte Carlo models of the system in scattered light. The models demonstrate that the observed flux distribution arises not from a disc but from a circumstellar envelope with an evacuated bipolar cavity. The envelope has a mass of 0.1-0.3 M⊙ within a radius of 670 au, and shows no evidence of a significant population of large dust grains.

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.