Astronomical instrumentation

Abstract:

Although most of the luminosity of Seyfert galaxy nuclei is emitted in the IR, the relative amounts of thermal dust and non-thermal emission are uncertain. Seyfert galaxies generally have smooth and featureless IR spectra, in contrast to the prominent dust emission features seen in galaxies whose nuclei resemble giant H II regions - the star burst nuclei1,2. Nevertheless, in type 2 Seyferts, the general form of the energy distribution and lack of marked variability suggest that here too thermal dust emission is dominant 3-5, and in NGC1068 this supposition is supported by the resolved size of its nucleus6. Dust is observed in absorption at 10 m (refs 7,8) and in emission near 20 m (ref. 9). Polarization has been detected from the UV to 10 m, and attributed to scattering and absorption at short wavelengths10 with a possible non-thermal component11,12, to scattering and non-thermal radiation in the near IR9, and to either absorption or non-thermal emission in the 10 m region13. We present here spectropolarimetric measurements of NGC1068, between 8 and 13 m, which show that the polarized flux at these wavelengths is intrinsic to the emission mechanism and not due to absorption by aligned grains. © 1984 Nature Publishing Group.

Abstract:

Four 8 - 13 μm spectra of the dust emission from Nova Aquilae 1982 are presented. The data, obtained between 140 and 280 days after outburst, show a prominent silicate emission feature superposed on a smooth warm continuum. The presence of the silicate grain signature, which is similar to laboratory emissivity curves of amorphous olivine smoke, indicates that these grains originated in an oxygen-rich environment where graphite or other carbon-rich grains are unlikely to have formed.

Abstract:

The infrared spectra of the type II OH/IR source OH 32.8 - 0.3 are presented, showing evidence for absorption bands near 12 and 3.1 microns. The 12 micron absorption feature is similar to that seen in OH 231.8 + 4.2 and is attributed to relatively pure water ice formed in the outflow from an evolved star.

Abstract:

From an examination of the published 8-13 micron spectra of galactic sources which show the unidentified emission features at 8.65 and 11.25 microns, and which are not heavily obscured, relationships between the feature equivalent widths and the depth of 10 micron minimum are established. Using these relationships a procedure is suggested for estimating extinction to objects whose 10 micron spectra are complicated by the presence of the features and the method is applied to the sample of 12 emission-line galaxy nuclei for which 10 micron spectra exist.

Abstract:

In the present investigation of the 10-micron extinction towards six WC8 or WC9 Wolf-Rayet stars, all objects are noted to show smooth dust emission having Si absorption whose depths are well correlated with extinction in the visible. The extinction to the stars is found to be predominantly interstellar in origin, with little being due to the circumstellar shell. The shape of the silicate absorption is better represented by a curve that is derived from the circumstellar dust shell of the M supergiant Mu Cep, than by that from the Trapezium in Orion. The A(v)/tau(9.7) ratio of 18.5 that is presently obtained holds over at least two directions in the galactic plane, as well as within the local 3 kpc.