Astronomical instrumentation

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.

Abstract:

Spectra of nuclei in the active galaxies NGC 1614, 7469 and 1275 are presented. The Ne II fine structure line and the 11.25 micron feature are observed in a NGC 7469 Seyfert nucleus and the high luminosity emission-line nucleus of NGC 1614. Observations are found to be consistent with no large optical extinction, although the 11.25 and 8.65 micron emission features make doubtful quantitative estimates of extinction based on the 10 micron minimum. Silicate absorption interpretation of the 10 micron minimum for M82 and NGC 1614 requires massive visual extinction, while the spectrum of NGC 7469 indicates no large internal extinction. Such features in the type 1 Seyfert NGC 7469 and 1614 indicate a dust-emission mechanism, while the featureless spectrum of NGC 1275 may arise from mechanisms such as synchrotron radiation, greybody thermal emission or self-absorbed silicate emission.