Prof Patrick Roche

Abstract:

8-13-micron spectra of eight moderately extended planetary nebulae have been obtained at a resolution of 0.24 micron using a 20-arcsec circular aperture. More compact planetaries which have been studied in this way generally show a strong continuum due to emission from dust, together with fine structure line emission. In contrast, these more extended objects have very weak continuum emission, and are dominated by fine structure line emission, especially by S IV forbidden lines which in several cases accounts for most of the broad-band 10-micron flux. There appears to be very little warm (equal to or greater than 150 K) dust in some of these objects.

Abstract:

The authors present infrared spectrophotometry of 20 symbiotic stars, mostly of the dust-rich variety. HDE330036 is unique in showing an emission feature at 11.3 μm. The remainder combine a hot grey component and/or optically thin silicate emission. A model in which the grey component is due to optically thick silicate dust is not consistent with the spectra. The authors propose instead that iron-based grains, expected to form in the ejecta of cool stars, are heated by the ultraviolet radiation field of the hot companion.

Abstract:

An 8-13 micron spectrum of the planetary nebula IC 2165 is presented. In addition to a bright S IV forbidden emission line, weak emission from the A III and Cl IV fine structure forbidden lines and the H7-6 hydrogen recombination line is identified. These lines are used to derive ionic abundances which are in agreement with those expected from the known excitation of the nebula. The rather weak continuum is attributed to free-free emission near 8 microns, but with increasing contributions from dust emission with increasing wavelength. From the presence of emission from silicon carbide dust, it is inferred that the emitting dust grains were formed in a carbon-rich environment, in accord with abundance determinations from optical and ultraviolet line emission.

Abstract:

High spatial resolution spectral observations of the planetary nebula NGC 7027 in the 10-micron region are reported. These show that the unidentified infrared features at 8.65 and 11.25 microns originate from a more extensive region than the shell of ionized gas; the data are consistent with these features arising entirely from the contiguous neutral region. This situation places further constraints upon a fluorescent excitation mechanism (Allamandola, Greenberg and Norman, 1979) and it is argued that the features are due to thermal emission from surface bonds on graphite grains in an H I region (Barlow, 1982, in preparation; Dwek et al., 1980).