Prof Patrick Roche

Abstract:

Spectropolarimetry of the 3.4 μm aliphatic C-H stretch feature, generally attributed to carbonaceous dust in the diffuse interstellar medium, has been carried out in the line of sight from the Galactic center source Sagittarius A IRS 7. The feature is unpolarized (Δp/Δτ < 0.2): the upper limit for polarization is well below that expected on the basis of a model in which the carrier molecules are associated with the aligned silicate component of interstellar dust, for example, as an organic or carbonaceous mantle on a silicate core. The simplest explanation is that the 3.4 μm carrier resides in a population of small, non-polarizing carbonaceous grains, physically separate from the silicates and sharing many characteristics with the carriers of the 217.5 nm extinction bump.

Abstract:

The properties of the carbon and oxygen chemical balance in planetary nebulae (PNe) are analysed through mid infrared spectroscopy of warm dust emission features in a sample of 72 objects. The adoption of a statistical distance scale shows that the galactic disk distribution of warm dust types in PNe is rather homogeneous with height over the galactic plane, and that there is a trend for the proportion of PNe with O rich dust signatures to decrease with galactocentric radius. Models of the galactic distribution of PNe compositions require a minimum progenitor mass of 1.2 M., although the observational constraints suffer from the smallness of the sample. This initial investigation is however an incentive to pursue the use of warm dust emission in PNe to study their progenitor population in various galactic environments.

Abstract:

Science workshops were held throughout the Gemini partnership during the second half of 1997 with the aims of identifying and quantifying the supporting capabilities required to enhance the utility and efficiency of the Gemini 8m telescopes. These workshops, held separately in the US, UK, Canada and South America, ensured representation programs were considered in detail sufficient to understand the requirements for their execution on Gemini as well as for any preparatory observations. The desire for wide-field optical and near-IR imaging was frequently identified with an average of one-half to one night of these survey observations per night of Gemini follow-up. Two other common themes were high angular resolution imaging and rapid response to target-of-opportunity events. ©2003 Copyright SPIE - The International Society for Optical Engineering.

Abstract:

We present near-infrared broad-band and H2 images of the quadrupolar source IRAS 04302+2247. High-resolution data at 3.8 μm show that the circumstellar envelope has a high degree of axisymmetry: the asymmetry at shorter wavelengths is almost certainly the result of extinction by dust in the cavity. Photometry of the flux peaks confirms that the source is variable but little change in appearance is observed between 1995 November and 1997 September. We report the first clear detection of the molecular outflow in H2 at 2.1 μm, revealing discrete streams which are inclined to the axis of the cavity. The motion of knots in the outflow remains the most likely cause of the variability.