Astronomical instrumentation

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.

Abstract:

Spectra at 8 - 13 μm of five spiral galaxies with giant H II regions in their nuclei are presented. The spectra are remarkably similar in showing the [Ne II] 12.81 μm fine structure line accompanied by strong emission features at 8.65 and 11.25 μm. The latter features are commonly associated with solid state transitions on dust grains, and thus provide direct evidence that dust emission dominates the infrared radiation of these objects. The spectra of all five galaxies show a minimum near 10 μm, which in several cases probably contains a contribution from silicate absorption. Extinction values calculated from optical and infrared emission lines ratioed against Hβ indicate only moderate reddening (A$_v$ = 0 - 5 mag). In most of the galaxies, this is far less than the extinction derived from the depth of the minimum in the 8 - 13 μm spectra, even after applying a correction for the contributions from the strong emission features.

Abstract:

The results of extensive IUE monitoring of the optical counterpart of the recurrent periodic LMC X-ray transient A0538-66 are presented. Even when the system is not in outburst dramatic spectral variations occur, accompanied by changes in the temperature and surface area of the continuum emitting region. It is shown that, in spite of these variations, the out-of-outburst data are consistent with constant bolometric luminosity. The optical outbursts can be powered solely by reprocessed X-rays. The long-term and orbital behavior of the system is discussed in the light of these results. From an analysis of apparently undisturbed P Cygni profiles, the mass-loss rate of the primary via its stellar wind is determined to be about 4 x 10 to the -9th solar masses/yr. Infrared photometry reveals an excess at H and K which is too large to be explained by free-free emission from this wind alone.