Dust Halo Research Articles

Toward understanding the fate of dust lost from the Martian satellites

We have investigated the dynamics of small dust grains ejected from the Martian satellites, considering both the solar radiation perturbation and electromagnetic forces since the grains move in a magrietized plasma. Lorentx forces can dramatically change the nature of the trajectories, resulting in, for example, prolonged for submicron‐slzed grains moving through our idealized iaodel. Though temporal changes of the solar wind were ignored and we only followed grains for 20 days or less, we suggest that a permanent, non‐uniform and time‐dependent dust halo of grains predominantly around 0.1 μm may exist about Mars.

Modeling of dust halo formation following comet outbursts: Preliminary results

Modeling of dust halo formation following comet outbursts: Preliminary results

Modeling of dust halo formation following comet outbursts: Preliminary results

Evolution of gas and dust distributions following a spatially and temporally localized comet outburst was calculated using a hybrid kinetic ‐ hydrodynamic method. It was found that a comet outburst resulted in significantly increased dust terminal velocities. As these higher terminal velocity values result in larger apex distances, therefore the outburst generates distinct dust envelopes in front of the regular dust coma. Such envelopes were observed at several comets (cf. comet Donati).

Submillimetre observations of the cold dust halo of NGC 7027

We report the detection of sub millimetre radiation from the planetary nebula NGC 7027. The measured flux at 370 μm is in excess of that expected from extrapolating the free–free emission of the H II region and the dust emission seen at 100 μm. This excess is interpreted as arising in a cold (∼ 20 K) dust halo surrounding the planetary nebula. We compare the 370-μm dust optical depth with the gas column densities and optical extinction to NGC 7027. The dust grains responsible for the submillimetre halo emission are similar to those found elsewhere in the interstellar medium, both in the ratio of the visual extinction efficiency to the absorption efficiency at 370 μm and in the abundance relative to the gas. The mass of dust required to produce the 370-μm excess is consistent with the halo mass of ≳ 5M ⊙ deduced by Knapp et al. (1982). This supports their conclusion that the masses of some stars which evolve into white dwarfs rather than supernovae are at least ∼6.5M ⊙ . This is consistent with the suggestion of Weidemann & Koester (1983) that white-dwarf progenitors can have masses up to ∼8M ⊙ .

Evidence for X-ray scattering by interstellar dust

X ray images of distant point sources obtained with the Einstein Observatory have been examined for the presence of halos produced by X-ray scattering from interstellar dust. Evidence for detection of dust halos has been obtained by comparing the apparent surface brightness in images of four low-latitude galactic center sources with the surface brightness predicted from the telescope point response function and the simultaneously measured source spectra. This evidence is considerably strengthened by the same comparison using images of two sources at higher galactic latitude, where the column density of dust is expected to be far lower. Simple assumptions indicate the observed scattering halos are consistent with production by the population of dust grains inferred from optical extinction measurements.

Evidence for the detection of X-ray scattering from interstellar dust grains

Overbeck1 has shown that small angle scattering of X rays by interstellar dust will tend to increase the apparent size of a point celestial X-ray source, the result being the formation of a halo around the source image. Although the exact description of this halo, which depends on the detailed properties of the dust and of the source, has been discussed2–6 no direct observational evidence for the existence of such haloes has been presented, although dust scattering has been invoked to explain the diffuse soft X-ray emission observed around the Crab Nebula during a lunar occultation7.I report here data obtained by the imaging proportional counter on board the Einstein Observatory8 of the bright X-ray source GX339–4 (4U1658–48). These data show a faint but apparently real X-ray halo around GX339–4. The principal uncertainty in the intensity distribution of the halo arises from the poorly determined spectrum of GX339–4 and it is likely that the parameters of the halo and of the derived model of the scattering dust grains may be improved in a future analysis using revised Einstein spectral calibration data; however, the range of allowed spectra leaves the reality of this first detection of an interstellar dust halo unchanged.

The photochemistry and dynamics of a dusty cometary atmosphere

A self-consistent solution of the dynamical and thermal structure of an H2O-dominated, two-phase, dusty-gas cometary atmosphere has been obtained by solving the simultaneous set of differential equations representing conservation of number density, momentum and energy together with the transfer of solar radiation in the streams responsible for the major photolytic processes and the heating of the nucleus. The validity of the model is restricted to the collision-dominated region where all the gas species are assumed to attain a common velocity and common temperature. Two models are considered for the transfer of solar radiation through the circum-nuclear dust halo. In the first only the direct extinction by the dust is considered. In the second, the finding of some recent models, that the diffuse radiation field due to multiple scattering by the dust halo more or less compensates for radiation removed by direct absorption when the optical depth is near unity, is approximated by neglecting the attenuation of the radiation by the dust altogether.

Dust in the universe

view Abstract Citations (12) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dust in the universe? Margolis, S. H. ; Schramm, D. N. Abstract The possible existence of intergalactic dust with properties similar to interstellar dust is examined in some detail. If such dust does exist, it could result in a correction to the observed deceleration parameter. The relation of the dust to possible intergalactic gas is examined, including survival times in a hot gas. The possible origins of intergalactic dust are also discussed. It is shown that uniform filling of the universe with dust is exceedingly unlikely, whereas dust halos around galaxies and clusters of galaxies may be quite likely. The dust optical depth across a cluster halo is estimated to be approximately 0.1. Publication: The Astrophysical Journal Pub Date: June 1977 DOI: 10.1086/155256 Bibcode: 1977ApJ...214..339M Keywords: Cosmic Dust; Cosmology; Intergalactic Media; Optical Thickness; Astronomical Models; Density Distribution; Galactic Clusters; Gas Temperature; Halos; Hubble Diagram; Hydrogen Plasma; Universe; Astrophysics full text sources ADS |

Implications of the colour distribution in the galaxy M82

AbstractPhotographic measurements of the colour distribution in the irregular galaxy M82 are presented and interpreted in terms of a model of that galaxy. Two alternative models are discussed. In the first the galaxy consists of a disc of highly reddened OB‐stars, whose scattered light is also seen in the halo, and a bulge of less reddened A—F stars. The direction of the inclination of the system, as inferred from this model, is opposite to that of LYNDS and SANDAGE (1963). The alternative inclination (second model) may possibly be preserved if one assumes a central dust ellipsoid reemitting scattered light from a central source of OB stars.If the velocities of the line emitting material refer to scattering particles, an inward motion of them is more probable than an outward one, irrespectively of the model, and the (dust) halo of the galaxy is probably contracting.