Spatial Distribution Of Dust Research Articles

Out-of-ecliptic distribution of interplanetary dust derived from near earth flux

The out-of-ecliptic distribution of interplanetary dust, i.e. its number density, mainly has been subject to optical or infrared remote sensing techniques. As the population in interplanetary space is made up of orbiting particles which will cross the ecliptic plane, determination of their orbital properties there gives a possibility also to derive their out-of-ecliptic distribution. Determination of orbital elements is provided by advanced detectors capable of measuring the vector of impact velocity. In a simple model, which applies for advanced detectors in near earth orbit, the feasibility of the method to determine the out-of-ecliptic spatial distribution of dust has been tested.

Spatial Distribution and Color of Dust in Halley’s Inner Coma

AbstractComposite images of the intensity of solar radiation scattered by dust in Halley’s coma are constructed by using the three-channel spectra obtained during the approach phase of the Vega 2 spacecraft. They cover a sector centered on the nucleus that has a radius of 40000 km and an angular extent of 50°. A radial plot of dust-scattered intensity shows that it varies as the inverse of impact parameter p where p is smaller than 3200 km or higher than 7000 km. In the intermediate 3200-7000 km distance range, the intensity varies as p−1.52. At longer distances, two jets are present with a contrast comparable to the gas jets which appear in the OH and CN images.The color of dust shows a slight excess of near-UV radiation in a diffuse region between 10000 and 30000 km which appears to be connected with the two jets. In the region called “valley”, between the jets at distances p > 25000 km, the dust-scattered intensity shows an excess of red. The color, expressed as the ratio of intensities at 377,482 and 607 nm is interpreted in terms of Mie theory. It is suggested that the dust particles progressively differentiate. A proportionally more important population of small submicronic grains appears at p > 8000 km. This population seems to correlate with the jets.

A subdued interpretation of the visual and infrared emission from merging galaxies - Application to NGC 6240

Les images URJHK de la galaxie en coalescence NGC 6240 sont presentees. La distribution de la luminosite et de la masse stellaire de la galaxie et la contribution de la population vieille au chauffage de la poussiere interstellaire sont analysees.

Emission from Dust Near High-Latitude Stars

The spatial distribution of interstellar dust is clearly important in understanding not only galactic dynamics but also the processing of the dust and the interstellar medium in general. Probably the best spectral region for investigating interstellar dust is the infrared (IR), where the cool dust is likely to radiate. Indeed, one of the most prominent features of the IRAS sky is the ubiquitous cirrus emission, thought to be due to interstellar dust heated by the interstellar radiation field (ISRF), seen at 60 and 100 μm (Low 1984). However, it is difficult to use the cirrus to probe the dust distribution, both because we have no depth information and also because the cirrus, due to its low temperatures (~20 K), is a probe of high-density dust regions. A far more sensitive search could be made if the dust were hotter, that is, in the presence of a greater ultraviolet (UV) flux. We have made use of this fact to search for dust in the vicinity of hot, bright stars, where even a small amount of dust will dominate the total emission along that line of sight.

The Infrared Brightness of the Ecliptic Plane

Prerequisite to the determination of the Galactic and Extragalactic contributions to the infrared background is an accurate removal of the zodiacal emission. The all-sky observations by IRAS in 1983 were made with a variety of observing conditions and with higher sensitivity and angular resolution than previous infrared and optical observations of the zodiacal background. These facts alone mandate a better understanding of the optical properties and spatial distribution of interplanetary dust.

Bow shocks and bubbles are seen around hot stars by IRAS

Examination of the IRAS all-sky imagery reveals extended, arcuate, and ringlike features associated with hot luminous stars. They fall into a number of classes: stellar wind bow shocks, stellar wind bubbles, dust shells, dust heated by isolated B stars, bright rims, and dust in H II regions. Here, some objects are discussed in which the star exercises structural control over the spatial distribution of dust: bow shocks, bubbles, and radiation pressure-driven shells. A list of the 15 most prominent objects is presented, a few prototypes are shown, and their characteristics are explained in terms of thermal emission processes and gasdynamics.

Optical probing of comet Halley from the Giotto spacecraft

The Halley optical probe experiment (HOPE) aboard the Giotto spacecraft has provided the first measurements of the optical properties of the dust and of some gaseous species (CN, C2, CO+ and OH) from inside the coma of comet Halley. The dust spatial distribution, inferred from sunlight scattering, obeys an r−2 law for distances from the nucleus r⩾2,000 km. The more rapid increase of dust density with distance observed in the innermost coma probably reflects the presence of a jet, or a surge of activity within a few hours before closest approach. The CN and OH signals increase more slowly than the dust signals, but faster than predicted by a simple model (of solar-excited resonance fluorescence) for the distribution of these species1. This effect is probably caused in part by the dust contribution, as well as by the production from parent molecules of OH and CN in an excited state.

Dynamics and Spatial Distribution of Interplanetary Dust

AbstractThree attempts to explain the radial power law distribution n(r)~r−1.3 of interplanetary dust are reviewed, which include the influence of Poynting-Robertson effect, collisions and interplanetary magnetic fields. Electromagnetic forces are unlikely to affect appreciably the spatial distribution. The replenishment of the cloud of interplanetary dust by the disruption of larger meteoritic particles in catastrophic collisions appears to give the most natural explanation for the observed spatial distribution.

Extinction in inhomogeneous clouds

view Abstract Citations (146) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extinction in inhomogeneous clouds. Natta, A. ; Panagia, N. Abstract An investigation is carried out on the effects of the spatial distribution of dust in the line of sight to an extended source on observed extinction. Consideration is given to a continuous dust cloud layer and one divided into clumps. An analytical relation is defined between the dust distribution parameters and the extinction. The extinction curve is analyzed as a function of wavelength, particularly with respect to the 2200 A bump and the H-alpha/H-beta ratio. A technique is derived for determining both the intrinsic extinction properties and geometric dust distribution using the observed extinction curve and is illustrated with the H II region K3-50. Extinction for the region is projected to be caused by both interstellar and local dust. Publication: The Astrophysical Journal Pub Date: December 1984 DOI: 10.1086/162681 Bibcode: 1984ApJ...287..228N Keywords: Hydrogen Clouds; Interstellar Extinction; Interstellar Matter; Nebulae; Stellar Spectrophotometry; Asymptotic Methods; Integral Equations; Near Infrared Radiation; Poisson Density Functions; Stellar Radiation; Astrophysics full text sources ADS | data products SIMBAD (1)

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 concentrationng≈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 50–300μ 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 λ=100μ and the same for the Perseus cluster near λ≈50–70μ. The total fluxes of IR emission from these clusters are about 105–106 Jy and can be detected by modern observational methods.

The integral equation approach to the study of interplanetary dust

Some considerations about the zodiacal light brightness integral from the stand point of the theory of integral equations are made. It is shown that for observation directions confined to a plane perpendicular to the ecliptic and passing through the Sun, the Z.L. brightness integral can be formally considered as a first kind integral equation of Volterra type (V.I.E.). In a second step, this equation is transformed into a V.I.E. of the second kind, from which, and under certain assumptions, the spatial distribution of dust out of the ecliptic is obtained.

Cometary dust observations by optical in-situ methods

Remote optical observations of comets provide information only along the whole line of sight and require some assumptions to be interpreted. Due to the advent of cometary space missions, a two-step strategy has been defined to derive without any assumption spatial distribution and physical properties of dust by in-situ optical observations. First, an Optical Probe Experiment , suitable for a fast fly-by, should provide passive in-situ measurements in the direction of the approaching (or receding) comet near encounter; by suitably differencing such observations, the brightness and polarization per unit volume can be recovered along the trajectory of the spacecraft. Secondly, a Light Scattering Dust Analyzer , suitable for a rendez-vous mission, should permit the determination of the scattering properties of individual particles . Both experiments also provide a connecting link between non-optical in-situ measurements (from mass spectrometers or impact detectors) and remote optical observations.

Recent developments in space-borne zodiacal light photometry

The 1985 International Solar Polar Mission will provide the first opportunity to perform measurements from out of the ecliptic and from above the solar poles. Included in this mission is the Zodiacal Light/Background Starlight Experiment of the Ruhr-University Bochum, FRG (in collaboration with the State University of New York at Albany). The experiment is based on the use of a multicolor, sky-scanning photopolarimeter, which will be carried on the NASA S/C. The scientific objectives of the experiment are to investigate the intensity, polarization, and color of the diffuse sky brightness and determine the spatial distribution and physical properties of the interplanetary dust, including a possible interstellar component, as a function of S/C position in and out of the ecliptic. The instrument will allow simultaneous measurements in two separate wavelength bands. Measurements will be performed at 180, 220, 240, 280, 320, 350, 360, 440, 540, 640, 800 nm, including the state of polarization. Two different fields-of-view (1 sq deg and 5.6 sq deg) can be selected. The use of a microprocessor system in the instrument electronics will provide flexibility in measurement sequences and programs, on-board data processing and data quality control.

The diffuse UV background

The diffuse radiation field in the UV (900–3,000 A) affects the structure of galactic molecular clouds and conveys important information concerning the physical characteristics and spatial distribution of gas and dust in the Universe. Continuum emission in this range is probably dominated by interstellar dust scattering in our Galaxy. For view directions and angular resolutions allowing observations in the rifts between galactic dust clouds, the background due to the integrated light of spiral galaxies may be detected, providing important information on their structure ana evolution. The redshifted emission from an intergalactic medium maybe observable in the regions between nearby bright galaxies. Present observations provide weak constraints on the radiation field required to ionize the intergalactic medium at the level required by the Gunn–Peterson test.

Dynamics of Micrometeoroids

Recent observations of zodiacal light have established a reliable and consistent picture of the spatial distribution of interplanetary dust in the ecliptic plane. The spatial density nr varies with heliocentric distance r according to a power law nr ∝ r−ν. From Helios observations an exponent v = 1.3 is derived for the distance interval from 0.08 A.U. to 1 A.U. (Link et al. 1976). Outside the earth's orbit the Pioneer 10 and 11 results suggest a higher exponent v = 1.5 for the distance interval from 1 A.U. to 3.3. A.U. (Hanner et al., 1976). Giese and Grün (1976) showed that the results from zodiacal light observations are compatible with the micrometeoroid fluxes derived from in situ measurements and lunar crater statistics. They found that micrometeoroids in the size range from 10 μm to 100 μm radii (corresponding roughly to 10−8g to 10−5g) contribute most to the zodiacal light brightness.The orbital distribution of large interplanetary particles (10−6 g < m < 10−3g) is known from meteor observations. Sekanina and Southworth (1975) reported average orbital elements of these particles: ā ∼ 1.25 A.U., ē ∼ 0.4 and ī ∼ 20°. Orbital information on micrometeoroids (m < 10−8g) is obtained from in situ detectors on board the Pioneer 8 and 9 and Helios 1 spaceprobes and the HEOS-2 satellite. Characteristics of the different micrometeoroid experiments are given in Table 1. There is almost no time overlap in the data taking intervals of the experiments. Therefore one has to assume that there are no time variations of the meteoroid flux on the time scale of 1 to 10 years if one compares the results from the different experiments. This assumption may be violated for the smallest of the observed particles (m < 10−13g) due to strong electromagnetic interaction of these particles with the interplanetary magnetic field (Morfill and Grün 1979).

The solar corona

view Abstract Citations (8) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The solar corona. Beard, D. B. Abstract The physical behavior of interplanetary dust and electrons has been examined with a view to anticipating their spatial distribution and consequent contribution to the intensity of the solar corona. From consideration of 'local' spherical expansion of the solar wind an electron distribution with solar distance r is proposed, r to the -2 power exp (W/r), which results in an excellent fit to observations of the solar corona and electron density at 1 AU. Analysis of total coronal observations during maximum and minimum solar activity at polar and equatorial elongations yields a time-constant spatial distribution of interplanetary dust in the equatorial plane beyond a minimum distance of closest approach of the dust of 4.5 solar radii. Several significant clear-cut deductions about the origin of the solar wind may be made from the expression for the electron density. Publication: The Astrophysical Journal Pub Date: December 1979 DOI: 10.1086/157546 Bibcode: 1979ApJ...234..696B Keywords: Interplanetary Dust; Solar Corona; Solar Electrons; Electron Density (Concentration); Solar Activity; Solar Wind; Spatial Distribution; Solar Physics; Interplanetary Dust:Distribution; Interplanetary Dust:Solar Corona; Solar Corona:Electrons; Solar Corona:Models; Solar Wind:Velocities full text sources ADS |

THE INFRARED SPECTRA OF NGC 7027 AND BD +30 3639.

ABSTRACT We have measured 20-33 fluxes for the planetary nebulae NGC 7027 and BD +30 3639 and have found significant discrepancies with respect to previously published data for that spectral region. Our observations of NGC 7027 blend smoothly with infrared data at shorter and longer wavelengths, and therefore we infer that ad hoc assumptions about grain emissivity or the spatial distribution of dust may not be required to match the infrared continuum. Our photometry also suggests that the dust boundary temperature is lower for NGC 7027 than for BD +30 3639. Key words: infrared sources - planetary nebulae

Radiative transfer in spherical circumstellar dust envelopes. IV - The infrared emissivity profile and composition of the dust in NGC 7027

Using radiative transfer methods described in the previous papers of this series, dust-emission models of the bright planetary nebula NGC 7027 have been calculated. An analysis of the infrared continuum of NGC 7027 based upon these calculations shows the following: If the spatial dust distribution coincides with the ionized gas distribution as given by Scott in 1973 (within approx.3.2'' from the center), the infrared continuum may be produced by an unknown substance whose infrared emissivity declines with increasing wavelength to about 50 $mu$ and then rises. If there exists a cool outer dust shell beyond 5''-6'' from the central source, the observed infrared continuum may be produced by iron grains of radius 1 $mu$ or by a mixture of smaller iron and graphite grains. (AIP)

On the origin of noctilucent clouds: Extraterrestrial dust and trapped water molecules

Estimates of the seasonal variations of the spatial distribution of mesospheric dust of extraterrestrial origin have been made by analyzing the expected meridional trajectories of incoming extraterrestrial dust particles. High-latitude summer conditions are of particular interest because of the expected relation between the presence of mesospheric dust and visual observations of noctilucent clouds. The predicted spatial distribution of the incoming extraterrestrial dust is germane to a mechanism proposed for the formation of noctilucent clouds whereby the settling dust nuclei effectively act to sweep down the condensable water to provide a substantial enrichment of the moisture content at altitudes where noctilucent clouds are formed.

Spatial Distribution of Interplanetary Dust

Interplanetary dust can be defined as solid particles outside Earth's atmosphere in the size range larger than a molecule and smaller than an asteroid. It is studied by a number of quite different techniques. For Earth-based observers, these techniques include measurement of the brightness and polarization of the interplanetary light, optical radar studies of particles entering the upper atmosphere, photographic and radar meteor observations, study of meteorites, and various methods of collecting dust particles in the atmosphere, in ice cores, and in deep sea sediments. Observations made from spacecraft include some interplanetary light observations and measurements of individual particles by means of microphones, penetration sensors, and collection experiments. These observational techniques are described by Millman (1969) and Bandermann (1969).