The infrared emission bands. III. Southern IRAS sources.

We present airborne 5-8 micrometers spectra of southern IRAS sources which reveal strong polycyclic aromatic hydrocarbon (PAH) emission features. The good correlation between the bands, in particular the dominant 6.2 and "7.7" micrometers features, strongly imply a common carrier, reinforcing the PAH hypothesis. However, small but detectable spectral variations exist. Planetaries have a distinctly different ratio of I(6.2)/I(7.7) than other nebulae, accompanied by a redward shift in the actual wavelength of the "7.7" micrometers peak. Further, we have detected a new feature, previously predicted from laboratory spectra of PAH molecules, at 5.2 micrometers in many of these sources. Spectra of two rare [WC 10] planetary nebular nuclei indicate a very prominent plateau of emission, linking the 6.2 and 7.7 micrometers bands. Several of our sources show definite evidence for emission structure between 14 and 23 micrometers in their IRAS Low-Resolution Spectral Atlas spectra: we attribute this structure to PAH bands. too. We have defined the "generic" spectrum of emission bands relating the mean intensities of each band to that of the strongest, near 7.7 micrometers. We have added three more planetary or protoplanetary nebulae to our correlation between 7.7 micrometers band intensity and nebular gas phase C/O ratio, namely NGC 6302, HR 4049, and the highly carbon-rich [WC 10] nucleus, CPD--56 degrees 8032. For the latter we have determined a ratio for C/O of approximately 4.8 from IUE observations. The good correlation between the intensity ratio of the "7.7" micrometers feature relative to the far-infrared dust continuum and nebular C/O also supports a carbonaceous carrier for these emission features.

Airborne and groundbased spectrophotometry of comet P/Halley from 5-13 micrometers.

Spectrophotometry from 5-10 micrometers (delta lambda/lambda approximately 0.02) of comet Halley was obtained from the Kuiper Airborne Observatory on 1985 December 12.1 and 1986 April 8.6 and 10.5, UT. 8-13 micrometers data were obtained on 17.2 December 1985 from the Nickel Telescope at Lick Observatory. The spectra show a strong broad emission band at 10 micrometers and a weak feature at 6.8 micrometers. We do not confirm the strong 7.5 micrometers emission feature observed by the Vega 1 spacecraft. The 10 micrometers band, identified with silicate materials, has substructure indicative of crystalline material. The band can be fitted by combining spectra data from a sample of interplanetary dust particles. The primary component of the silicate emission is due to olivine. The 6.8 micrometers emission feature can be due either to carbonates or the C-H deformation mode in organic molecules. The lack of other emission bands is used to place limits on the types of organic molecules responsible for the emission observed by others at 3.4 micrometers. Color temperatures significantly higher than the equilibrium blackbody temperature indicate that small particles are abundant in the coma. Significant spatial and temporal variations in the spectrum have been observed and show trends similar to those observed by the spacecraft and from the ground. Temporal variability of the silicate emission relative to the 5-8 micrometers continuum suggests that there are at least two physically separated components of the dust.

Spectra, Variability, Size, and Polarization of H2O Microwave Emission Sources in the Galaxy.

Radio spectral line radiation of water molecules at a wavelength of 1.35 centimeters has been measured from eight sources in the galaxy. The sources are less than I arc minute in diameter, have extremely high brightness temperatures, and show many spectral features. Some spectral features are slightly polarized and some have changed greatly in intensity in a few weeks time.