Prof Patrick Roche

Abstract:

A new megamaser galaxy has been discovered as part of an OH survey of selected IRAS galaxies. This increases the number of known megamaser galaxies to seven, and extends the range of their infrared luminosity and colour temperature. The new megamaser differs from the others in that it appears optically as a spiral galaxy with a bright core, although the megamaser emission itself indicates that this core must contain an active nucleus. Both the infrared luminosity and the 60/100 K colour temperature are below those of any other OH megamaser galaxies, but the OH/infrared luminosity ratio is close to the median value, lending support to the suggested relationship between OH and infrared luminosities.

Abstract:

Spectra between 8-13 microns of 15 planetary nebulae are presented. Those planetaries with strong continuum emission are classified according to their dust emission spectra as oxygen or carbon rich. The spectrum of NGC 6302 shows a very strong emission line at 7.65 microns, confirming the reality of the feature seen by the low-resolution spectrometer on IRAS. The data presented here bring the number of available 8-13-micron spectra to 49. The far-infrared properties of planetary nebulae are found to reflect the differences in the dust chemistry found from the 8-13-micron spectra. This dependence is clearly seen in color-color plots constructed from the IRAS data, so that the different grain materials seen in the 8-13 micron spectra also show differences in the dust emissivity at longer wavelengths.

Abstract:

Spectra are presented with a resolving power λ/Δλ \ap 1100 of the dusty Wolf-Rayet star Ve 2-45 and the southern H II region G333.6-0.2. An upper limit on the equivalent width of any features in the range 11.0 to 13.0 μm is determined to be 0.0022 μm towards Ve 2-45. This figure is compared with the predicted strength of the unobserved narrow feature at 11.52 μm which has been proposed to be associated with small graphite grains (Draine).

Abstract:

Speckle observations at the peaks of narrow dust emission features at 3.3 and 3.5 microns in the low-excitation planetary nebula CPD-56 deg 8032 and the peculiar emission-line star HD 97048 are presented. In CPD-56 deg 8032 the emission in the 3.28-micron band is extended on a scale of approximately 1.3 arcsec, and this is probably the same as the extent of the ionized nebula. By contrast, the emission in the 3.53-micron band in HD 97048 is spatially unresolved and arises from a region less than 0.1 arcsec across. Dust grains within 0.05 arcsec of the star have temperatures not less than 1000 K, so that the proposed identification of the species emitting the strong 3.43-and 3.53-micron features with formaldehyde ice is untenable, and the materials responsible for the band emission remain unidentified.

Abstract:

The results of 8-13 micron spectropolarimetric observations of Galactic Center sources are presented. All the sources show interstellar polarization due to absorption by aligned silicate grains, and these grains appear to be spatially separated along the line-of-sight from those which produce the polarization at shorter wavelengths. The line of sources IRS 1, 10, 5, and 8 comprising the northern arc all show strong intrinsic polarization due to thermal emission from aligned grains of amorphous silicate-like material. This polarization is very uniform among these sources with position angle closely normal to the line of the arc. It is shown that the data are inconsistent with grain alignment due to streaming, but favor alignment by a strong magnetic field greater than 10 mG directed along and linking the northern arc of sources. A field of this magnitude will have significant influence on the structure and evolution of sources in the Galactic Center. Some possible implications are discussed.