Astronomical instrumentation

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.

Abstract:

Photometry and 2-4 and 8-13 micron spectrometry of Nova Aquilae 1982, obtained during its dust shell phase are presented. The photometry indicates that, if dust formation ocurred in the outburst ejecta, it did so at an anomalously early stage of the outburst; alternatively the dust shell may have predated the eruption. Spectrometry at the shorter wavelengths suggests the presence of broad, weak features, whilst that in the 8-13 micron window shows strong emission from siicate grains. This indicates that, unlike the situation in previous dusty novae, the grains around Nova Aquilae formed in an oxygen-rich environment. The difference between this nova and others observed in the infrared to date may thus provide clues to differing elemental abundances in classical nova progenitors. On the other hand, this object may not have undergone a normal classical nova outburst.

Abstract:

Spectra at 8-13 micron of 10 Seyfert galaxy nuclei, roughly equally divided between types 1 and 2 and the quasar 3C 273, are presented. These sources show no evidence for dust emission features, with the exception of the type 2 Seyfert NGC 7582, which does show the narrow dust emission features at 8.65 and 11.25 micron. Two of the other type 2 Seyferts, NGC 1068 and 5506, have minima near 10 micron, attributed to absorption by cold silicate dust. The remainder have smooth featureless spectra well fit by power laws. The lack of dust emission features is in remarkable contrast to nonactive galaxy nuclei and luminous Galactic H II regions. If dust emission is responsible for the radiation from Seyfert nuclei and from 3C 273, silicate grains are absent or are too cold to radiate significantly below 13 micron while any infrared featureless grains are required to radiate strongly and must exist over a wide range of temperatures.