Infrared spectra of small interstellar grains

It is shown that surface stresses in small particles will lead to a broadening and weakening of strong resonances in the infrared spectrum of interstellar dust.     

Infrared spectra of carbonaceous chondrites and the composition of intertellar grains

Gravitational instability of an infinitely conducting hydromagnetic composite rotating plasma is considered to include simultaneously the finite Larmor radius effects and the frictional effects with neutrals. It is found that Jeans' criterion of instability holds good in the presence of rotation, finite Larmor radius and collisions with neutrals. The particular cases of the above effects on the waves propagated along and perpendicular to the magnetic field have been discussed. The effect of rotation is to decrease the Larmor radius by an amount depending upon the wave number of perturbation.     

Optical spectra of amorophous carbon grains

Extinction coefficient measurement of amorphous carbon grain, produced by hydrocarbon buring, have been carried out at room temperature in the spectral range from 1900 Å to 2.5 . The classical KBr pellet technique has been used to obtain quantitative data. Corrections to accout for matrix distorsion of the spectrum have been determined experimentally by measuring the spectrum of the same grains deposited on a thin quartz plate.     

Infrared emission from interstellar grains heated by supernovae

The infrared emission from interstellar grains heated by a supernova in eruption is investigated. The dependence of the emission on various physical parameters, such as the depth of the supernova into the dust plane of the parent galaxy, the inclination of the galaxy to the line-of-sight, are investigated. The possibility of detecting this emission is discussed. The prospects are hopeful as far as cryogenically-cooled instruments in Earth orbit are concerned.     

Infrared low-resolution spectra of symbiotic stars

The IRAS low-resolution spectra (LRS) of 29 symbiotic stars are presented in this paper. It is found that silicate dust is common material in the circumstellar shells of symbiotic stars. From the IRAS low-resolution spectra, IRAS colors, symbiotic types and spectral types, some physical properties of symbiotic stars with the LRS spectra are also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Infrared reflectance spectra of Martian analogues

Reflectance spectroscopy in the infrared is a powerful tool to characterise the optical properties of analogue materials for Mars. In this work we present laboratory studies of four Martian analogues: calcite, montmordlonite, palagonite and andesite. Diffuse and specular reflectance and transmittance spectra in the IR are shown. The spectral effect produced by small grains clung to the larger ones is analysed for calcite. Significant variations in the diffuse reflectance spectrum, especially in the reststrahlen region, are observed. The diffuse reflectance spectra of the other materials show the shift of the reststrahlen features with Si content in the materials. Optical constants of andesite are retrieved, by using the Lorentz model, from the specular reflectance spectrum. These values are fundamental in performing modelling of the radiance coming from the planet Mars.     

Infrared spectra of cooling flow galaxies

We have taken K -band spectra covering seven cooling flow clusters. The spectra show many of the 1-0S transitions of molecular hydrogen, as well as some of the higher vibrational transitions, and some lines of ionized hydrogen. The line ratios allow us to conclude that the rotational states of the first excited vibrational state are in approximate local thermodynamic equilibrium (LTE), so that densities above 10⁵ cm⁻³ are likely, but there is evidence that the higher vibrational states are not in LTE. The lack of pressure balance between the molecular gas and the ionized components emphasizes the need for dynamic models of the gas. The ratios of the ionized to molecular lines are relatively constant but lower than from starburst regions, indicating that alternative heating mechanisms are necessary.     

Infrared emission of dust grains in the clusters of galaxies

The observations of the reddening of the distant galaxies and the weak diffuse radiation in the clusters of galaxies can be interpreted as a consequence of the presence of dust grains in the intergalactic medium. When allowance is made for the destruction of the grains in collision with particles of the hot gas, its lifetime is about 10⁷–10⁸ yr at a gas concentrationn _g 10^–3 cm^–3. The detection of the infrared (IR) emission from the galaxy clusters might be the test for the proof of the presence of dust grains in the intergalactic medium. In this paper the estimates of the expected intensities and fluxes of IR emission for the spectral region 50–300 are presented for two galaxy clusters in Coma and Perseus. The parameters of the hot gas spatial distribution are chosen from X-ray observations. Having assumed that intergalactic dust can be ejected only from the galaxies, we used such a model for intergalactic dust grains which explains very well the interstellar dust effects. It is shown that the dust temperature, which is determined from the general energetic balance of the dust grains, can achieve some scores of degrees of Kelvin. Two models of the dust spatial distribution are considered. It is found that the maximum of IR flux for the Coma cluster lies near =100 and the same for the Perseus cluster near 50–70. The total fluxes of IR emission from these clusters are about 10⁵–10⁶ Jy and can be detected by modern observational methods.     

Infrared spectra of quasars and related objects

An attempt is made to explain the infrared radiation observed for several quasars and Seyfert galaxies as thermal radiation of a dust envelope surrounding the cores of these objects. Two kinds of dust particles (graphite and silica) are taken into consideration. It is shown that the observed spectral behaviour and the luminosity in the infrared can be introduced as thermal radiation of silica grains. In the case of 3C 273 one finds that the radius of the dust envelope is about 50 pc and the total mass of dust is about 600M _⊙.     

Origin of cometary extended sources from degradation of refractory organics on grains: polyoxymethylene as formaldehyde parent molecule

The radial distribution of some molecules (CO, H₂CO, HNC, …) observed in the coma of some comets cannot be explained only by a direct sublimation from the nucleus, or by the photolysis of a detected parent compound. Such molecules present a so-called extended source in comae. We show in this paper that extended sources can be explained by refractory organic material slowly releasing gas from grains ejected from the cometary nucleus, due to solar UV photons or heat. The degradation products are produced throughout the coma and therefore are presenting an extended distribution. To model this multiphase chemistry we derive new equations, which are applied to Comet 1P/Halley for the case of the production of formaldehyde from polyoxymethylene (POM), the polymer of formaldehyde (-CH₂-O-)_n. We show that the presence of a few percent of POM on cometary grains (a nominal value of ∼4% in mass of grains is derived from our calculations) is in good agreement with the observed distribution, which so far were not interpreted by the presence of any gaseous parent molecule.     

Infrared imaging spectroscopy with micron resolution of Sutter's Mill meteorite grains

Synchrotron‐based Fourier transform infrared spectroscopy and Raman spectroscopy are applied with submicrometer spatial resolution to multiple grains of Sutter's Mill meteorite, a regolith breccia with CM1 and CM2 lithologies. The Raman and infrared active functional groups reveal the nature and distribution of organic and mineral components and confirm that SM12 reached higher metamorphism temperatures than SM2. The spatial distributions of carbonates and organic matter are negatively correlated. The spatial distributions of aliphatic organic matter and OH relative to the distributions of silicates in SM2 differ from those in SM12, supporting a hypothesis that the parent body of Sutter's Mill is a combination of multiple bodies with different origins. The high aliphatic CH₂/CH₃ ratios determined from band intensities for SM2 and SM12 grains are similar to those of IDPs and less altered carbonaceous chondrites, and they are significantly higher than those in other CM chondrites and diffuse ISM objects.     

Grain size dependence of far-infrared extinction spectra of amorphous fine grains

The far-infrared extinction spectra of fused silica grains with the size range from 1.8 m to 60 Å were measured. The spectra depend clearly on the grain size. For large grain sizes (from 1.8 m to 400 Å) the spectra show almost the ^–2 dependence ( is the wavelength), which resembles that of the bulk material. For fine grains (70 and 60 Å) the spectra are less steep, the wavelength dependence being ^–1. This grain size dependence of extinction spectra agrees essentially with the prediction of Seki and Yamamoto.     

Infrared spectra of evolved stars with unusual dust shells

New mid-infrared spectra are presented of a number of oxygen-rich evolved stars which have IRAS LRS (Low Resolution Spectrometer) spectra that were classified as showing SiC emission. Two of the sources, IRC−20445 and IRC−20461, show the unidentified infrared (UIR) bands superposed on silicate emission features. Both objects have been classified as M supergiants. Several other sources show three-component spectra, with peaks at 10, 11 and 13 μm. The 13-μm source FI Lyr shows a narrow emission feature at 19 μm. Emission by oxide grains may be responsible for the 11-, 13- and 19-μm features. One object, IRC−20455, shows a self-absorbed silicate feature. There is no clear evidence for SiC emission in any of the spectra: the LRS spectra were erroneously classified as showing SiC emission because of the relatively strong 11-μm emission.     

Infrared reflectance spectra of Hyperion,Titania, and Triton

Medium-resolution infrared (1–2.5 μm; Δλ/λ ∽ 0.05) photometry of Triton, Titania, and Hyperion and medium-resolution (1.5–2.4 μm; Δλ/λ ? 0.01) spectroscopy of Triton are presented. Hyperion and Titania have spectra roughly similar to the laboratory spectrum of water frost, while the spectrum of Triton is inconsistent with the spectra of frosts likely to be major surface constituents.     

Infrared hydrogen emission lines in the spectra of Be stars

For the interpretation of observed hydrogen emission lines in the spectrum of Cas calculations of the relative intensities of spectral lines of the Balmer, Paschen, Brackett and Pfund series are carried out, by using the theory of moving stellar envelopes.It is shown that in the spectra of Be stars, which have opaque envelopes and therefore a slow Balmer decrement, infrared hydrogen lines must be relatively strong.It is also found that the observed relative line intensities of Cas are in qualitative agreement with those calculated for the case of a simple model-envelope which consists of low and high opacity regions.     

Laboratory production of monophase pyrrhotite grains using solid-solid reaction and their characteristic infrared spectra

A new method of producing pyrrhotite grains, which are most commonly found in cometary material and interplanetary dust particles, was developed. Pyrrhotite grains in the monophase having a 7C structure were predominately produced using a solid-solid reaction between iron and sulfur grains at room temperature. The characteristic infrared peaks were observed at 602, 563, and 397 cm⁻¹ (16.6, 17.8, and 25.2 μm).     

Infrared diffuse reflectance spectra of carbonaceous chondrites: Amount of hydrous minerals

Abstract— Infrared diffuse reflectance spectra (2.53–25 μm) of some carbonaceous (C) chondrites were measured. The integrated intensity of the absorption bands near 3 μm caused by hydrous minerals were compared with the modal content of hydrous minerals for the meteorites. The CM and CI chondrites show larger values of the integrated intensity than those of the unique C chondrites Y82162, Y86720 and B7904, suggesting that the amount of hydrous minerals in the CM and CI chondrites is larger, which supports the contention that hydrous minerals were dehydrated by thermal metamorphism in the unique chondrites. Orgueil (CI) has the largest value of the integrated intensity among the C chondrites we measured and shows a sharp absorption band at 3685 cm^?1 (2.71 μm) that is not seen in the spectra of the CM chondrites. There is an excellent correlation between the observed hydrogen content in C chondrites and the integrated intensity. The CM chondrites show a wide variation in the strength of absorption bands at 1470 cm^?1 (6.8 μm), despite the similarity in absorption features near 3 μm for all CM chondrites. The 1470 cm^?1 band could be due to the presence of some hydrocarbons but may also be a result of terrestrial alteration processes.     

Infrared spectra of gaseous mononitriles: Application to the atmosphere of Titan

A list of volatile nitriles, not yet detected in the atmosphere of Titan, but likely to be present in this environment, has been selected: acetonitrile, propionitrile, acrylonitrile, crotononitrile, allyl cyanide, methacrylonitrile, and cyanopropyne. The spectra of these compounds in the gas phase have been systematically studied, in the mid- and far-infrared ranges. For each selected nitrile, the most intense vibration bands have been determined. Their strengths have been characterized by estimating the monochromatic absorption coefficient at the maximum(s) of the bands, and the integrated absorbance over the entire band. Then, in order to estimate the detectability of the selected compounds by infrared spectroscopy in the atmosphere of Titan, the data obtained have been extrapolated to the case of Titan.     

Infrared transmission spectra from 2.5 to 25 μm of various meteorite classes

Infrared transmission spectra from 53 meteorites in the spectral range from 2.5 to 25 μm were measured to permit comparisons with data of astronomical objects that are potential meteorite sources. Data were taken for 14 carbonaceous chondrites, 5 LL ordinary chondrites, 6 L ordinary chondrites, 10 H ordinary chondrites, 1 enstatite chondrite, 4 aubrites, 3 eucrites, 4 howardites, 1 diogenite, 1 mesosiderite, 2 nakhlites, 1 shergottite, and the anomalous achondrite Angra dos Reis. The CO and CV carbonaceous chondrites have spectra similar to each other, with 10-μm features characteristic of olivine. The CM carbonaceous chondrites have distinctive 10-μm features that are attributed to layer lattice silicates. Members of both the CI and CR classes have spectra distinct from those of other carbonaceous chondrites. The LL, L, and H ordinary chondrites have spectra that match those of olivine and pyroxene mixtures. The enstatite chondrites and enstatite achondrites (aubrites) all exhibit spectra diagnostic of the pyroxene enstatite. The angrite, howardites, aucrites, nakhlites, shergottite, and diogenite all have similar spectra also dominated by pyroxene. The single mesosiderite examined had a spectrum distinct from all the other meteorites.