[en] Spectra covering the 7-23 μm region of the M2Ia star α Orionis have been obtained with the IRAS Low Resolution Spectrometer. These, together with IRAS photometric data and previously published microwave data, have been used to develop a model of the star's outer atmosphere and circumstellar shell. (author)

[en] 8-13 μm spectra of eight moderately extended planetary nebulae have been obtained at a resolution of 0.24 μm using a 20-arcsec circular aperture. More compact planetaries which have been studied in this way generally show a strong continuum due to emission from dust, together with fine structure line emission. In contrast, these more extended objects have very weak continuum emission, and are dominated by fine structure line emission, especially by [S IV] which in several cases accounts for most of the broad-band 10 μm flux. There appears to be very little warm (>approx.= to 150 K) dust in some of these objects. (author)

[en] Spectrophotometry at 8-13 μm of Mkn 231 confirms that the 10 μm minimum is due to large columns of silicate dust in the line-of-sight to the nucleus. Fits to the detailed spectral shape demonstrate that the cool absorbing grains are at the emission (z=0.042) rather than the absorption (z approx.= 0.025) redshift and are located within the nuclear region. (author)

[en] A distinctive feature of the HH46/47 outflow field in the long straight 'jet-filament', which emerges from the globule encasing the stellar source to form a bridge between a number of discrete Herbig-Haro objects. The high-velocity flow detected along this filamentary channel excites patches of nebulosity, designated HH47BN, HH47A and HH47D, at roughly equal intervals along the track. Recent observations show an additional curved filament emerging from the globule and crossing the high-velocity flow at HH47BN. It is shown in this paper that the main features of the region, such as the geometries of the patches of nebulosity and their spacing, can be understood if the curved filament is a portion of a far more extensive helical structure which touches the straight channel at intervals. The similarly curved configuration of HH47C in the opposite hemisphere suggests that a related structure threads the counterflow. (author)

[en] The spectra of M-supergiants in the 7-100 μm region are considered as part of a study of late-type stars based on the IRAS Low Resolution Spectrometer Catalogue. The circumstellar silicate dust features at 9.7 and 18 μm are observed to be of variable width. Most stars exhibit the classical circumstellar silicate dust features, typified by those of a Ori, modelled in a previous paper. Some stars exhibit much broader features, VXSgr being the brightest example. The latter stars can be fitted with a similar model, where the continuum is shown to be dominated by free-free emission. Dust condensing within outflows from various oxygen-rich stars generally produce similar emission characteristics, suggesting that the dust grains have a similar composition. This study shows that the strength of the spectral emission features produced by circumstellar dust in the infrared are correlated with surface temperature and luminosity, but not with pulsation characteristics of the stars. (author)

[en] The band strengths of 11.2μm SiC features in IRAS spectra have been determined for a number of carbon stars whose mass-loss rates have been determined earlier from the COJ=2→1 or J=1→0 emission lines. The strength of the 11.2μm SiC feature is proportional to the total mass-loss rate (as measured from CO), supporting the idea that the gas-to-dust ratio is roughly constant for carbon stars. This therefore provides an easy method of calculating mass-loss rates for carbon stars which are too distant to be detected in CO. The observed correlation probably also indicates that the ratios of carbon to silicon carbide grains in the outflows increase with age. (author)

[en] The band strengths of the 9.7 μm circumstellar silicate dust features have been obtained for a number of oxygen-rich red giant and supergiant stars whose mass loss rates have been determined using the CO (J = 2-1) and (J = 1-0) emission lines. We show that the strength of the 9.7 μm silicate dust feature is directly proportional to the mass loss rate (so long as the feature remains optically thin), indicating that the dust-to-gas ratio is approximately constant for oxygen-rich stars. The silicate dust feature thus provides a method of measuring mass loss rates for oxygen-rich red giants and supergiants, which are too distant to be detected in CO. (author)

[en] We describe a number of red giants which are classified as type M (i.e. oxygen-rich) but which are defined in the IRAS LRS Catalog as having SiC emission (a characteristic of carbon-rich environments). We show that the near-infrared spectra are characteristic of oxygen-rich stars, but that at least some appear to have carbon-to-oxygen abundance ratios close to unity (in other words they should be classified as S stars). We suggest that when C/O approaches unity, dust condensation theories assuming chemical and thermodynamic equilibrium may not be realistic. It is postulated that a number of carbon stars which have been found to have silicate dust features may also have C/O abundance ratios close to unity. These conclusions are all supported by near-infrared spectra which in each case confirm the optical classifications of the stars. (author)

[en] Four 8-13μm 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. (author)

[en] 8-13 μm spectra 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 μm. Two of the other type 2 Seyferts, NGC 1068 ad 5506, have minima near 10 μm, attributed to absorption by cold silicate dust. The remainder have smooth featureless spectra well fit by power laws. (author)