Astronomical instrumentation

Abstract:

Spectra of the central core and surrounding coma of Comet IRAS-Araki-Alcock (1983d) were obtained at 8-13 μm on 11 May and 2-4 μm on 12 May 1983. Spatially resolved measurements at 10 μm with a 4-arcsec beam showed that the central core was more than 100 times brighter than the inner coma only 8 arcsec away; for radially outflowing dust, the brightness ratio would be a factor of 8. The observations of the central core are consistent with direct detection of a nucleus having a radius of approximately 5 km. The temperature of the sunlit hemisphere was > 300 K. Spectra of the core are featureless, while spectra of the coma suggest weak silicate emission. The spectra show no evidence for icy grains. The dust producton rate on 11.4 May was ∼ 105 g/sec, assuming that the gas flux from the dust-producing areas on the nucleus was ∼ 10-5 g/cm2/sec. © 1985.

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.