Optical properties of particulates

Optical properties of small particles of olivine (less than 0.1 μ) have been studied in the ultraviolet as an example of an insulating solid. Very little structure survives in the ultraviolet extinction curves for such small particles. By contrast ‘surface modes’, observed for graphite small particles in the ultraviolet and for olivine particles in the infrared, produce dominant and persistent structure in extinction. The general trend of optical properties of graphite is surprisingly similar to the behavior required to explain all features of the interstellar extinction and albedo curves from near visible to 1000 Å. Measured extinction of small olivine particles in the infrared agrees with calculations based on newly measured optical constants, but dominant sharp structure in the 10μ region still presents a bit of a problem in explaining ‘silicate’ features in astronomical data.     

Optical properties of dust grains

In this paper we present new and exact analytical and computational developments of Güttler's formulae for composite grains, thereafter applied for the two models:

Photometric properties of zodiacal light particles

From published ground-base, spacecraft, and rocket photometry and polarimetry of the zodiacal light, a number of optical and physical parameters have been derived. It was assumed that the number density, mean particle size, and albedo vary with heliocentric distance, and shown that average individual interplanetary particles have a small but definite opposition effect, a mean single-scattering albedo in the V band at 1-AU heliocentric distance of 0.09 ± 0.01, and a zero-phase geometric albedo of 0.04. Modeled by a power law, both albedos decrease with increasing heliocentric distance as r^?0.54. The corresponding exponents for changes in mean particle size and number density are related in a simple way. The median orbital inclination of zodiacal light particles with respect to the ecliptic is 12°, close to the observed median value for faint asteroids and short-period comets. Furthermore, the color of dust particles and its variation with solar phase angle closely resemble those of C asteroids. These findings are, at least, consistent with the zodiacal cloud originating primarily from collisions among asteroids. Finally, a value of ?10¹⁸?_ErmE g was derived for the mass of the zodiacal cloud, where ?_E is the mean particle radius (in micrometers) at 1-AU-heliocentric distance. For extinction in the ecliptic, $\text{Δm = 10}{}^{\mathrm{?5}}\text{?}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}\text{mag}$ was obtained, where ? is the solar elongation in degrees.     

Optical properties of circumstellar silicate grains

The optical properties of circumstellar silicate dust grains around oxygen-rich giant stars are investigated with close attention to infrared observations of OH/IR stars. The optical constants are deduced from available astronomical and laboratory data. The deduced opacities at longer wavelengths (12 m) for OH/IR stars are higher than the one for M-type Miras possibly because of the change of optical constants depending on temperature of dust grains. Absorption and scattering efficiencies are evaluated for various grain size distributions and shapes. The results of detailed radiative transfer model calculations based on our dust parameters are compared with observational data. The Planck mean values incorporating substantial far-infrared absorption are also calculated.Yonsei University Observatory Contribution No. 91.Department of Astronomy and Space Science, Chungbuk National University Contribution No. 4.     

Infrared properties of haze particles of Venus

The computed variation of the infrared flux and polarization of Venus as a function of phase angle, based upon multiple-scattering calculations for the cloud model of Kawabata et al. (1980) with an internal heat source, precludes the possibility of sulfuric acid as the composition of the haze particles located above the main cloud. Furthermore, our calculations reveal that the hazticle should have a large absorption coefficient at these wavelengths, i.e, $\text{k(}\text{imaginary part of the complex refractive index}\text{) ? 1.3}\text{at a wavelength}\text{λ = 3.4 μ}\text{m}$. The optical thickness of the haze layer must be about 0.15 at λ = 3.4 μm.     

Optical properties of aerosols in Titan's atmosphere

In the frame of fractal modeling of tholin aggregates we made a systematic analysis of their optical properties. Ballistic particle-cluster aggregation (BPCA) and diffusion-limited aggregation (DLA) of spherical primary particles (monomers) identical in material composition were considered. Aggregates composed of identical particles (monodisperse cluster), as well as of size-distributed particles (polydisperse cluster), were simulated. To calculate the light-scattering models, the code based on the superposition T-matrix method is used. Orientationally averaged properties of light scattering by model particles were extracted, and the normalized phase function and the degree of linear polarization were calculated as functions of scattering angle. We concluded that: (a) aggregation mechanism as well as specific internal structure of the clusters play only a minor role, and for the future it is not necessary to investigate aggregates of different types; (b) the intensity is very sensitive both to the size parameter of forming particles x and to the size parameter of the aggregates X; (c) characterization of the aggregates by the number of monomers is insufficient to retrieve physical properties of aggregates from optical measurement; and (d) it is very desirable to include into the analysis polarization data calculated for the different clusters.     

Optical properties of low z radio galaxies

The optical morphological and photometric properties of 79 low redshift radio galaxies are discussed. It is found that most radio galaxies are luminous bulge dominated systems similar to normal non-radio giant ellipticals. The average absolute magnitude of the sample is 〈M_HOST(tot)〉=−23.98, with a clear trend for FR I sources to be ∼0.5 mag brighter than FR II galaxies. In about 40% of the objects we find an excess of light in the nucleus attributable to the presence of a nuclear point source. This contributes on average for ∼1–2% of the total flux from the host galaxy. Radio galaxies follow the same μ_e−R_e relationship of normal (non-active) elliptical galaxies. The distribution of ellipticity, the amount of twisting and shape of isophotes do not differ significantly from other ellipticals. These results support a scenario where radio emission is little related with the overall properties of the host galaxy.     

Optical properties of single-component zodiacal light models

To provide material for interpretations of forthcoming zodiacal light measurements the characteristics of 468 single-component, in-ecliptic models are summarized in two survey diagrams. The models are based on Mie theory and on a power law dn ∞ r^?γα^?kdα for the dependence of the particle number density n on solar distance r and on the size parameter α (circumference/wavelength). The size range involves particles with α_min ≤ α ≤ 120; (α_min = 1,2,4,10,60), flat (k = 2·5) and steep (k = 4) size spectra, and complex refractive indices m = m₁ ? m₂i with m₁ = 1·33; 1·5; 1·7 and m₂ = 0; 0·01; 0·05; 0·1.The models suggest that the spatial variation of dust particle number densities should be less than about ∞ r^?0·5 in the ecliptic plane. Either dielectric particles of tenth-micron size or absorbing particles of half-micron size or very slightly absorbing particles of some tens of microns in size are able to produce polarization that agrees in sign and location of the maximum with the observations. Ambiguities can only be removed by considering intensity and polarization over a wide range of wavelengths.     

Some identities for spheroidal harmonics

The spheroidal harmonics expressions $$\left[ {P_{2k}^{2s} \left( {i\xi } \right)P_{2k - 2r}^{2s} \left( \eta \right) - P_{2k - 2r}^{2s} \left( {i\xi } \right)P_{2k}^{2s} \left( \eta \right)} \right]e^{i2s\theta } $$ and $$\left[ {\eta ^2 P_{2k}^{2s} \left( {i\xi } \right)P_{2k - 2r}^{2s} \left( \eta \right) + \xi ^2 P_{2k - 2r}^{2s} \left( {i\xi } \right)P_{2k}^{2s} \left( \eta \right)} \right]e^{i2s\theta } $$ , have ξ²+η² as a factor. A method is presented for obtaining for these two expressions the coefficient of ξ²+η² in the form of a linear combination of terms of the formP _2m ^2s (iξ)P _2n ^2s (η)e ^i2sθ. Explicit formulae are exhibited for the casesr=1, 2, 3 and any positive or zero integersk ands. Such identities are useful in gravitational potential theory for ellipsoidal distributions when matching Legendre function expansions are employed.     

Optical properties of dust from Jupiter family comets

To try to define specific physical properties of the dust of Jupiter-family comets (JFCs), we compare the light scattered by them. Amongst the more than 1000 JFCs, less than 200 are numbered, 40 of them being rather bright. In the present work we use data from the latter. In situ observations of three nuclei show low albedo surfaces. The albedo of the dust particles in the coma is low, with generally a red colour. The A(α)fρ product is a measure of cometary activity and secular changes. Images of different regions (jets and fans) give indications on the nucleus rotation and position of the emitting areas, as compared to the position of the rotation axis. Differences in physical properties between the particles in different regions are pointed out by differences in the linear polarization of the scattered light and by spectral variations in brightness and polarization. Jupiter family comets are considered as dust-poor comets. Tails and trails’ studies give an estimation of the size distribution of the particles. However the dust production rates depend on the largest particles (up to centimetre size), which are mainly observed in the trails where large dark compact particles are found. These dark particles are also responsible for the high polarization in the inner most coma of some comets. The meaning, in terms of physical properties, of the linear polarization is discussed through different examples such as 2P/Encke, 9P/Tempel 1 or the fragments of 73P/Schwassmann-Wachmann 3. Cometary outbursts and splitting events show that the properties of the dust ejected from the interior of the nucleus are similar to the ones of more active comets (new or with larger semi-major axis).     

Optical properties of silicates in the far ultraviolet

Near-normal incidence reflectance measurements in the interval 1026–1640 Å were performed on four silicates already studied in the visible and infrared by Pollack et al. (1973). We use a Kramers-Kronig analysis of these data to calculate the complex index of refraction m = n ? ik. New transmission measurements improve the determination of k in the interval 2500–4500 Å, except for andesite, which is more opaque than found by Pollack et al.     

Optical properties of some terrestrial rocks and glasses

The optical constants of five naturally occurring rocks have been determined in the spectral range between 0.2 and .50 μm. Between 0.2 and 5 μm, the real and imaginary parts of the index of refraction were found from a combination of reflectivity and transmission measurements by using Beer's law and the Fresnel reflectivity equation. At wavelenths beyond 5 μm only reflectivity measurements could be made and both constants were found from an application of classical dispersion theory. These optical constants will be valuable for studies of the interaction of light with rock surfaces, atmospheric dust and interplanetary and interstellar dust grains.     

Optical properties of Small Magellanic Cloud X-ray binaries

This work represent the first major study of the optical and infrared characteristics of the mass donor companions to the X-ray pulsars in the Small Magellanic Cloud (SMC). In this work several new counterparts have been identified, and possible ones confirmed, as companions to X-ray pulsars in the SMC giving a total of 34 such objects now identified. In addition this work presents three new binary periods and confirms two X-ray periods using optical data for objects in this group. This homogeneous sample has been studied as a group to determine important general characteristics that may offer an insight into the evolution of such systems. In particular, the spectral class distribution shows a much greater agreement with those of isolated Be stars, and appears to be in some disagreement with the galactic population of Be stars in Be/X-ray binaries. Studies of the long-term optical modulation of the Be star companions reveal an extremely variable group of objects, a fact which will almost certainly make a major contribution to the pronounced X-ray variability. The spatial distribution of these systems within the SMC is investigated and strongly suggests a link between massive star formation and the H  i density distribution. Finally, studies of the circumstellar disc characteristics reveal a strong link with optical variability offering important clues into the long-term stability of such discs.