Astronomical instrumentation

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.

Abstract:

A 10-micron spectrum of periodic Comet Grigg-Skjellerup was obtained on 22 June 1982 with the UCL array spectrometer at the United Kingdom Infrared Telescope, Mauna Kea. No emission feature is obvious in the spectrum. The observed spectrum can be fit equally well by a model of small hot absorbing grains or by a composite model with less than or equal to 30 percent (3sigma) warm, ’dirty’ silicate grains. The latter model is consistent with the silicate abundance in Comet Kohoutek, which did display an emission feature at 10 microns.