Prof Patrick Roche

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).

Abstract:

Infrared spectral observations of the Wolf-Rayet system Gamma Velorum in the atmospheric windows between 1.45 and 12 microns are presented. Results show an extremely rich emission line spectrum in which permitted lines of helium and carbon and forbidden lines of neon and sulfur are present, some of which have not previously been observed in any object. The relative abundances of He I/He II and C/He are estimated, and lower limits to the Ne/He and S/He abundance ratios are presented.

Abstract:

8-13 micron spectra are presented of 24 planetary nebulae and other emission line objects, 19 of which are published here for the first time. This brings the total of planetary nebulae for which such spectra are available to 23 including four classed as very low excitation (VLE) objects and three as WC-11 objects. On the basis of these spectra, roughly one-third of the planetaries are identified as having oxygen-rich (silicate) and rather less than one-third carbon-rich (silicon carbide) dust grains. Of the oxygen-rich nebulae, three are VLEs while the rest are very compact and, on various grounds, considered to be young. The remainder of the planetary nebulae exhibit strongly the unidentified feature at 11.25 microns and frequently that at 8.65 microns and their dust chemistry is uncertain. All of the 23 planetaries exhibit one or more of the fine structure forbidden lines of Ar III, S IV and Ne II roughly in accordance with their optical excitation class. The line intensities are consistent with approximately solar abundance of these elements.

Abstract:

Spectrophotometry from 8-13 microns of the strong infrared source in the nucleus of NGC 5253 indicates the presence of an obscured region of very high ionization. The shape of the dust continuum suffering from silicate absorption and the strength of the forbidden lines S IV fine structure line require either a compact cluster of several hundred early O stars or a single massive highly luminous object within 50 pc of the nucleus obscured in the visible, to provide both the infrared luminosity and ionizing flux. It appears that the infrared emission has been produced by a recent burst of star formation, probably with a bias towards more massive stars, and the 8-13 micron spectrum shows no evidence for the narrow emission features of 11.25 and 8.65 microns, or the forbidden lines Ne II line at 12.8 microns.