Prof Patrick Roche

Abstract:

An array spectrometer was used on the nights of 1985 May 30-June 1 to observe the disks of Uranus and Neptune in the spectral regions 7-14 and 17-23 μm with effective resolution elements ranging from 0.23 to 0.87 μm. In the long-wavelength region, the spectra are relatively smooth with the broad S(1) H2 collision-induced rotation line showing strong emission for Neptune. In the short-wavelength spectrum of Uranus, an emission feature attributable to C2H2 with a maximum stratospheric mixing ratio of 9 × 10-9 is apparent. An upper limit of 2 × 10-8 is placed on the maximum stratospheric mixing ratio of C2H6. The spectrum of Uranus is otherwise smooth and quantitatively consistent with the opacity provided by H2 collision-induced absorption and spectrally continuous stratospheric emission, as would be produced by aerosols. Upper limits to detecting the planet near 8 μm indicate a CH4 stratospheric mixing ratio of 1 × 10-5 or less, below a value consistent with saturation equilibrium at the temperature minimum. In the short-wavelength spectrum of Neptune, strong emission features of CH4 and C2H6 are evident and are consistent with local saturation equilibrium with maximum stratospheric mixing ratios of 0.02 and 6 × 10-6, respectively. Emission at 8-10 μm is most consistent with a [CH3D]/[CH4] volume abundance ratio of 5 × 10-5. The spectrum of Neptune near 13.5 μm is consistent with emission by stratospheric C2H2 in local saturation equilibrium and a maximum mixing ratio of 9 × 10-7. Radiance detected near 10.5 μm could be attributed to stratospheric C2H4 emission for a maximum mixing ratio of approximately 3 × 10-9. Quantitative results are considered preliminary, as some absolute radiance differences are noted with respect to earlier observations with discrete filters. © 1987.

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.