8–13 μm spectrophotometry of Comet Kohoutek

Spectrophotometry of Comet Kohoutek (1973f) covering the wavelength range 8–13 μm is presented. The spectral shape of the derived flux excess above a blackbody closely resembles that seen in circumstellar and interstellar dust and generally attributed to metallic silicates.     

Infrared spectrum of Io, 2.8–5.2 μm

The reflectance spectrum of Io is presented from 2.8 to 5.2 μm, extending the earlier results of D. P. Cruikshank, T. J. Jones, and C. B. Pilcher (1978, Astrophys. J. 225, L89–L92), and demonstrating the full extent of the broad and deep spectral absorption between 3.5 and 4.8 μm. Laboratory spectra of nitrates and carborates diluted with sulfur do not satisfactorily reproduce the Io spectrum, but new information based on the recently discovered volcanic activity on the satellite lead to consideration of other classes of compounds as reported in a companion paper (F. P. Fanale, R. H. Brown, D. P. Cruikshank, and R. N. Clark, 1979, Nature280, 761–763).     

Mid-IR (8–13 μm) images of the 21 μm,carbon rich proto-planetary nebulae

We present 9.7 and 11.8 m narrow band (/=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 m feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M hydrogen burning core star.     

Interstellar absorptions at λ=3.2 μm and 3.3 μm

Unidentified interstellar absorption bands at =3.2 m and 3.3 m might be due to amino-acids in bacterial grains.     

Observations of Jupiter and Saturn at 5–8 μm

Moderate-resolution spectrophotometry (Δλ/λ～0.015) has shown the effects of known atmospheric constituents (NH₃, CH₄, C₂H₆) on the 5–8 μm spectrum of Jupiter. Broadband observations of Saturn at 6.5 μm are also reported.     

Modelling The 5–30 μm Spectrum of Comet Halley

The 5–30 μm spectrum of Comet P/Halley is modelled for various grain compositions on the basis of an observationally determined distribution of grain sizes. We compute the distribution function of grain temperatures and fluxes arising from (1) a mineral grain model, and (2) an organic grain model comprised of a diatom/POM mixture. The organic/POM model yields excellent accord with the cometary observations. This revised version was published online in July 2006 with corrections to the Cover Date.     

The wavelength dependence of granulation (0.38–2.4 μm)

Using 2 pinhole photometers the intensity of the undisturbed photosphere was recorded simultaneously in 6 and in 4 wavelength regions. The rms value of the intensity variation in each of the 10 wavelength regions decreases slightly with increasing value of the heliocentric angle; this result confirms recent observations by other authors and supports the critique of the results given by Edmonds (1964).We report the detection of a secondary maximum in the wavelength dependence of the intensity variation at 1.5 m.     

The spectra of Uranus and Neptune at 8–14 and 17–23 μm

An array spectrometer was used on the nights of 1985 May 30–June 1 to observe the disks of Uranus and Neptune in the spectral regions 7–14 and 17–23 μm with effective resolution elements ranging from 0.23 to 0.87 μm. In the long-wavelength region, the spectra are relatively smooth with the broad S(1) H₂ collision-induced rotation line showing strong emission for Neptune. In the short-wavelength spectrum of Uranus, an emission feature attributable to C₂H₂ with a maximum stratospheric mixing ratio of 9 × 10⁻⁹ is apparent. An upper limit of 2 × 10⁻⁸ is placed on the maximum stratospheric mixing ratio of C₂H₆. The spectrum of Uranus is otherwise smooth and quantitatively consistent with the opacity provided by H₂ collision-induced absorption and spectrally continuous stratospheric emission, as would be produced by aerosols. Upper limits to detecting the planet near 8 μm indicate a CH₄ stratospheric mixing ratio of 1 × 10⁻⁵ or less, below a value consistent with saturation equilibrium at the temperature minimum. In the short-wavelength spectrum of Neptune, strong emission features of CH₄ and C₂H₆ are evident and are consistent with local saturation equilibrium with maximum stratospheric mixing ratios of 0.02 and 6 × 10⁻⁶, respectively. Emission at 8–10 μm is most consistent with a [CH₃D]/[CH₄] volume abundance ratio of 5 × 10⁻⁵. The spectrum of Neptune near 13.5 μm is consistent with emission by stratospheric C₂H₂ in local saturation equilibrium and a maximum mixing ratio of 9 × 10⁻⁷. Radiance detected near 10.5 μm could be attributed to stratospheric C₂H₄ emission for a maximum mixing ratio of approximately 3 × 10⁻⁹. Quantitative results are considered preliminary, as some absolute radiance differences are noted with respect to earlier observations with discrete filters.     

An integrated 2.5–12.5 μm emission spectrum of naturally-occurring aromatic molecules

The expected emission features from an ensemble of naturally-occurring aromatic molecules is shown to be in satisfactory agreement with the emission properties of PAH molecules associated with planetary nebulae.     

10 μm Imaging of the Blue Compact Galaxy HE 2–10

We present the first results of a survey of Blue Compact Galaxies with a 10 m array. Blue Compact Galaxies (BCGs) are dwarf galaxies experiencing an intense burst of star formation. As dwarf systems, their main characteristics is a low heavy-elements abundance. Although dust is thought to be less abundant in these galaxies than in normal spirals, the presence of a compact starburst region favors a detection in the infrared, and 10 m imaging is perfectly suited to star formation studies in BCGs since it focuses on the hottest dust inside the star-forming regions.     

Infrared diffuse reflectances (2.5–25 μm) of some meteorites

We measured emissionless infrared diffuse reflectances of some meteorites by using a Fourier transform infrared spectrophotometer to obtain additional information on identification of asteroidal surface materials. Although the spectral features of diffuse reflectances are apparently different from those of transmission spectra, the absorption bands of constituent minerals can be detected. C2 carbonaceous chondrite materials can be distinguished from C3 materials by the depth of their hydration bands around 3 and 6 μm. These hydration bands do not lose contrast by pulverization of the sample. Acid dissolution experiment shows that the 6.8-μm band in the spectra of the Murchison (C2) meteorite is probably due to carbonates. The enstatite meteorite examined (Norton County) shows absorption bands around 10 μm caused by pyroxene unlike the iron meteorite examined (Mundrabilla). Because these latter two meteorite types give similar spectra without strong absorption bands in the UV-Visible-near IR region, middle infrared spectra should be helpful in interpreting asteroidal surface materials when combined with the UV-Visible-near IR spectra.     

Organic material and the 2.5–4 μm spectra of galactic sources

The spectra of galactic infrared sources over the waveband 2.5–4 m provide clear evidence for an organic composition of interstellar grains.     

A Model of The 2–4 μm Spectrum of Comet Halley

Recent observations of Halley's Comet show a broad absorption band centred at 3.4 μm and which can be explained on the basis of a bacterial grain model. This revised version was published online in July 2006 with corrections to the Cover Date.     

An Integrated 2.5–12.5 μm Emission Spectrum of Naturally-Occurring Aromatic Molecules

The expected emission features from an ensemble of naturally-occurring aromatic molecules is shown to be in satisfactory agreement with the emission properties of `PAH molecules' associated with planetary nebulae. This revised version was published online in July 2006 with corrections to the Cover Date.     

Infrared spectroscopy over the 2.9–3.9 μm waveband in biochemistry and astronomy

The infrared spectrum of the galactic centre source IRS 7 over the 2.9–3.9 m waveband is interpreted as strong evidence for bacterial grains.     

2.8–3.6 μm Spectra of Micro-Organisms with Varying H2O Ice-Content

The extinction curves of bacterial grains on which variable mass fractions of water-ice are condensed are calculated. Because the ice band at 3.07 μm is stronger by a factor of about thirty than the OH and CH stretching bands in organic materials even a small mass fraction of ice condensed inside or on the surface of the particles modifies and tends to obscure the characteristic biological signature at ∼ 3.4 μm. This revised version was published online in July 2006 with corrections to the Cover Date.     

Infrared Spectroscopy Over The 2.9–3.9 μm Waveband in Biochemistry and Astronomy

The infrared spectrum of the galactic centre source GC-IRS 7 over the 2.9–3.9 μm waveband is interpreted as strong evidence for bacterial grains. This revised version was published online in July 2006 with corrections to the Cover Date.     

Silicon monoxide and the 10 μm interstellar feature

Laboratory spectra of SiO particles of 1 m radius show a broad structureless extinction peak at 9.6m. The wavelength dependence of extinction from SiO, an amorphous silicon oxide, provides a good match to that of interstellar dust.     

Correlation of simultaneous ultraviolet (0.36 μm) and infrared (8 to 14 μm) images of Venus

We present evidence for a correlation between features observed in simultaneous infrared (8 to 14 μm) and ultraviolet (0.36 μm) images obtained during Venus' 1975 and 1977 apparitions. The sense of the observed correlation is such that bright uv markings correspond to bright (warm) ir features, and similarly, dark uv markings correspond to dark (cool) ir features.     

2.4 μm emission from the galactic centre region

It is shown that the 2.6 mm CO emission profile in the regions of two unidentified 2.4 m features observed near the galactic centre is consistent with an explanation of these features in terms of inhomogeneities in interstellar extinction. From our observations we estimate the mass to luminosity ratio of the galactic central bulge to beM/L _v=4.