Dust Formation and Mass Loss in Evolved Stars

The problem of dust formation in the circumstellar envelopes of Asymptotic Giant Branch stars is addressed. We summarize the basic thermodynamic prerequisites necessary to enable the formation and growth of solid particles from the gas phase and draw some conclusions on the evolution of the emergent dust component. In a circumstellar environment the dust grains interact with the stellar radiation field, which leads to a strong coupling among the local thermodynamic conditions and the dust formation process itself. By a consistent treatment of the physics describing the dust forming circumstellar shells of evolved stars we demonstrate, that the non-linear interaction among the dust formation process and the hydrodynamic and thermodynamic conditions of the dust forming system leads to a complex dynamical structure of these shells. Some observable consequences resulting from corresponding model calculations are given. This revised version was published online in August 2006 with corrections to the Cover Date.     

SPECTROSCOPY OF A GEMINID FIREBALL: ITS SIMILARITY TO COMETARY METEOROIDS AND THE NATURE OF ITS PARENT BODY

A detailed analysis of a photographic spectrum of a Geminid fireball obtained in December 14, 1961 at the Ondrejov Observatory is presented. We have computed a synthetic spectrum for the fireball and compared it with the observed spectrum assuming chemical equilibrium in the meteor head. In this way we have determined relative chemical abundances in meteor vapors. Comparing the relative chemical abundances of this Geminid meteoroid with those obtained from meteoroids associated with comets 55P/Tempel-Tuttle and 109P/Swift-Tuttle we found no significant chemical differences in main rock-forming elements. Despite of this similarity, the deepest penetration of the Geminid meteoroids and their ability to reach high rotation rates in space without fragmentation suggest that thermal processing is affecting their physical properties. We suggest that as consequence of space weathering a high-strength envelope is produced around these particles. In this picture, heating processes of the mineral phases could result in the peculiar properties observed during atmospheric entry of the Geminid meteoroids, especially their strength, which is evidenced by its resistance to ablation. Finally, although one meteoroid cannot be obviously considered as representative of the composition of its parent body, we conclude that 3200 Phaethon is able to produce millimetre-size debris nearly chondritic in composition, but the measured slight overabundance of Na would support a cometary origin for this body.     

First-order effects of the Earth's oblateness upon coasting bodies

The Kustaanheimo-Stiefel transformation and perturbation techniques are employed in deriving approximate closed-form expressions for the trajectories of bodies coasting about an oblate Earth. The solutions are used to obtain Lambert type solutions which include oblateness effects.Research primarily supported by a NASA-ASEE Fellowship, supporting work with the Mission Planning and Analysis Division, Johnson Space Center.     

Tropospheric ozone chemistry. The impact of cloud chemistry

The effect of clouds and cloud chemistry on tropospheric ozone chemistry is tested out in a two-dimensional channel model covering a latitudinal band from 30 to 60° N. Three different methods describing how clouds affect gaseous species are applied, and the results are compared. The three methods are:

?A first order parameterization scheme for the removal of sulphur and other soluble gases by liquid droplets.

?A parameterization scheme for SO₂, O₃, and H₂O₂ removal is constructed. The scheme is based on the solubility of gases in liquid droplets, cycling times of air masses between clouds and cloud free areas and on the chemical interaction of SO₂ with H₂O₂ and O₃ in the liquid phase.

?Gas-aqueous-phase interactions and aqueous-phase chemical reactions are included in the reaction scheme for a number of components in areas where clouds are present.

In all three methods, a full gas-phase chemistry scheme is used. Particular emphasis is given to the study of how the ozone and hydrogen peroxide levels are affected. Significant changes in the distributions are found when aqueous-phase chemical reactions are included. The result is loss of ozone in the aqueous phase, with pronounced reductions in ozone levels in the middle and lower troposphere. Ozone levels are reduced by 10 to 30% with the largest reductions in the remote middle troposphere, bringing the values in better agreement with observations. Changes in H₂O₂ are harder to predict. Although, in one case study, hydrogen peroxide is produced within the aqueous phase, concentrations are mostly comparable or even lower than in the other cases. Hydrogen peroxide levels are, however, shown to be very pH sensitive. pH values around 5 seem to favour high H₂O₂ levels. High H₂O₂ concentrations may be found particularly in the upper part of the clouds under favourable conditions.     

ITERATIVE SOLUTION TO PERTURBED KEPLER PROBLEM VIA KUSTAANHEIMO–STIEFEL EQUATION

The main purpose of this paper is to supply a proof of formulas for constructing a perturbative solution to the perturbed Kepler problem by utilizing quaternion algebra of the Kustaanheimo–Stiefel formulation. The main advantage of this approach is a removal, from the corresponding solution, of fast oscillations (in the case of conservative forces) and small divisors (in the case of time-dependent forces). This revised version was published online in July 2006 with corrections to the Cover Date.     

Stratigraphic inversion of siliciclastic basin fills: a note on the distinction between supply signals resulting from tectonic and climatic forcing

Rates of accommodation and sediment supply are the principal controls on stacking patterns in siliciclastic basin fills. Stratigraphic inversion is aimed at reconstruction of these controls from the detrital record. Efforts to ‘explain’ siliciclastic basin fills have been focused on analysis and numerical modelling of sequence geometry in response to changes in accommodation, whereas comparatively few studies have attempted to address the role of sediment supply. The compositional and textural properties of siliciclastic basin fills are linked with the evolution of drainage basins through the principle of climatic–physiographic control of sediment production and supply. Application of this principle leads to a method of compositional analysis for distinguishing sequences controlled by high-frequency changes in the rate of accommodation from sequences controlled by high-frequency variations in the rate of sediment supply (order of 10 kyr). This method does not require detailed time control. Changes in rate and type of sediment supplied to depositional systems in response to environmental perturbations in drainage basins are explored in greater detail by means of a numerical model of sediment production under various scenarios of climatic and tectonic forcing. Simulation experiments suggest that drainage basins respond differently to high-frequency tectonic and climatic perturbations. Synthetic time series of cyclically forced sediment production display different types of asymmetric variations in grain size, accumulation rate and residence time of sediments in response to tectonic and climatic forcing. The results also highlight the role of vegetation as the principal modulator of climate forcing, and show that the nonlinear response to climate change may frustrate any attempts at providing broad generalizations of the system's responses. The modelling results confirm the usefulness of a combined analysis of sediment composition and sequence geometry, and the mathematically rich behaviour of the system suggests that further development of this approach is likely to increase our ability to reconstruct forcing mechanisms and initial boundary conditions from the detrital record.     

Determination of the geopotential scale factor from satellite altimetry

Summary The geopotential scale factor R ₀ =GM/W ₀ has been determined on the basis of satellite altimetry as R _{0=(6 363 672·5±0·3) m} and/or the geopotential value on the geoid W ₀ =(62 636 256·5±3) m ² s ^–2 . It has been stated that R ₀ and/or W ₀ is independent of the tidal distortion of surface W=W ₀ due to the zero frequency tide.

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¶rt;a nmu amumuu u ama amnmuaa R ₀ =GM/W ₀ =(6 363 672,5±0,3) m u/uu aunmuaa a nmuu¶rt;a W ₀ =(62 636 256,5±3) m² s^–2. m, m R ₀ u/uu W ₀ auum m nm amu a a nuu ¶rt;au nmu W=W ₀ .