Ramona Wegmann

ZHAW Zurich University of Applied Sciences | ZHAW · School of Social Work

Sublimation (vaporization) of the icy component of a cometary nucleus determines the initial composition of the coma gas as it streams outward and escapes. Photolytic reactions in the inner coma, escape of fast, light species such as atomic and molecular hydrogen, and solar wind interaction in the outer coma alter the chemical composition and the p...

Water chemistry is central in understanding the physics and chemistry of comets. It is the major source of ions and electrons via photochemistry that further initiate key gas-phase and electron impact reactions, leading to the plethora of molecules and atoms seen in cometary comae. In this paper, relevant physico-chemical processes in the coma of c...

This paper presents and studies Fredholm integral equations associated with the linear Riemann–Hilbert problems on multiply connected regions with smooth boundary curves. The kernel of these integral equations is the generalized Neumann kernel. The approach is similar to that for simply connected regions (see [R. Wegmann, A.H.M. Murid, M.M.S. Nasse...

The Deep Space 1 Mission successfully encountered comet 19P/Borrelly on 22 September 2001, returning a wealth of images and in situ plasma measurements. To enhance the scientific return of the mission, it is desired to gain knowledge of basic properties of the cometary environment through the interpretation and analysis of the spacecraft data. For...

Water chemistry is central to understanding physico-chemical mechanisms in comets. In situ measurements of comet Borrelly by the PEPE instrument onboard the Deep Space 1 spacecraft challenge our accepted notions of comet comae chemistry.

Water chemistry is central in understanding the physics and chemistry of comets It is a major source of ions and electrons that further initiate key gas-phase reactions leading to the plethora of molecules and atoms seen in cometary atmospheres The relevant physico-chemical processes are identified within a modeling framework to understand in situ...

This paper presents two new Fredholm integral equations associated to the interior and the exterior Riemann–Hilbert problems in simply connected regions with smooth boundaries. The kernel of these integral equations is the generalized Neumann kernel. The solvability of the integral equations depends on whether λ=±1λ=±1 are eigenvalues of the kernel...

The volume intensity of the cometary X-ray emission is enhanced behind the bow shock by a factor of up to three. This effect offers the opportunity to identify the bow shock by a tomographic method in X-ray images of comets. By an analysis of the X-ray data obtained by XMM-Newton from Comet C/2000 WM1 (LINEAR) we obtain information on the position,...

X-ray emission from comets is generated by charge exchange of heavy solar wind ions in a high ionization state with the neutral particles of the cometary coma. We use model calculations and theoretical considerations to study the morphology of the emission. The emission is located in a bowl-shaped region on the subsolar side of the nucleus. We deri...

X-ray emission from comets is generated by charge exchange of heavy solar wind ions in a high ionization state with the neutral particles of the cometary coma. We use model calculations and theoretical considerations to study the morphology of the emission. The emission is located in a bowl-shaped region on the subsolar side of the nucleus. We deri...

The Deep Space 1 Mission (DS1) successfully encountered comet 19P/Borrelly on 22 September 2001, and returned a wealth of unique information about its nucleus and surrounding environment. A coma model for 19P/Borrelly is presented that consistently represents the comet from the nucleus surface to the solar wind interaction region. Neutral gas and p...

The Deep Space 1 Mission (DS1) successfully encountered comet 19P/Borrelly on 22 September 2001 returning a wealth of images and in situ plasma measurements. A coma model for 19P/Borrelly is presented that consistently represents the cometary environment from the nucleus surface to the solar wind interaction region. Neutral gas and plasma dynamics...

Model calculations for the interaction of the solar wind with a comet are presented that extend 30 million km into the tail. It is shown that the disturbance of the interplanetary magnetic field (IMF) (the draping) is limited to timescales of 10 to 50 hours and length scales of 10 to 50 million km. This is supported by a theoretical argument about...

The Deep Space 1 Mission is scheduled to encounter comet 19P/Borrelly in September 2001. For the successful outcome of this mission, knowledge of basic properties of the cometary environment is needed. A comet coma model is presented for 19P/Borrelly that consistently represents the dusty cometary environment from the irregularly shaped nucleus sur...

A class of Riemann–Hilbert (RH) problems on multiply connected circular regions is treated iteratively by a method of successive conjugation (SC), which solves the problem on a single boundary circle each time, running through all circles in each iterative step. It is shown that the method converges. Convergence is linear with a rate which can be c...

A comet model is presented for 19P/Borrelly during the Deep Space 1 encounter. The model consistently represents the dusty coma from the irregularly shaped nucleus to the solar wind interaction region with detailed photo and gas-phase chemistry; dust entrainment by the gas with fragmentation and distributed gaseous sources; separate energy balance...

The effect of several solar wind disturbances on the plasma tail of a comet is studied by means of MHD model calculations. In particular, high speed streams (HSS) and non compressive density enhancements (NCDE) are investigated. Interplanetary shock waves, changes of the flow direction and current sheets are reconsidered. It is shown that HSSs, NCD...

An improved magnetohydrodynamic (MHD) model with chemistry is presented. The analysis of the source and sink terms for H2O + shows that for small comets up to 11% of water molecules are finally ionized. For large comets (such as Halley) this fraction decreases to less than 3%. From the MHD scaling laws a similarity law for the individual ion densit...

An iterative method is presented which constructs for an unbounded region G with m holes and sufficiently smooth boundary a circular region H and a conformal mapping Phi from H to G. With the usual normalization both H and Phi are uniquely determined by G. With a few modifications the method can also be applied for a bounded region G with m holes....

and Abstract. A two-and-a-half-dimensional two-ion fluid model (with gyrotropic pressure tensor) for the interaction of cometary pickup plasma with the solar wind has been developed. Whereas previous models have, in general, assumed a one-fluid plasma, this generalized model follows the evolution of two fluids: solar wind protons and cometary ions....

By means of axisymmetric hydrodynamic models with chemistry we study the X-ray emission of two processes in a comet: Bremsstrahlung of solar wind electrons interacting with the neutral gas coma, and charge exchange of heavy solar wind ions in high ionization states with the neutral cometary gas. Comparisons of morphology, intensity and spectrum wit...

Des Wissens bar, doch des Wunsches voll. Richard Wagner, Twilight of the Gods

We present a first attempt to model the profile of ion emission lines in a cometary plasma tail with the aid of a 3D-MHD model of the comet-solar wind interaction, and to compare the calculated line profiles to high-resolution measurements of the H_2_O^+^ doublet at 6159Å in comet 1P/Halley on January 6, 1986. The modelled line profiles are asymmet...

A two-ion fluid model (with gyrotropic pressure tensor) for the interaction of cometary pickup plasma with the solar wind has been developed. Whereas previous models have, in general, assumed a single fluid plasma, this generalized model follows the evolution of two fluids — solar wind protons and cometary ions. The two fluids are coupled by the ma...

An upstream differencing numerical scheme is devised for the double-adiabatic equations which describe a plasma with anisotropic pressure. The Godunov-type method uses an approximate Riemann solver, which is constructed with an explicit representation of the complete eigensystem of the Jacobian matrix of the flux vector. A correction term is introd...

The iterative method of Wegmann (1978) for conformal mapping of a region E to a region G is reformulated in terms of a conjugation operator. If the boundary of G is sufficiently smooth, the method converges quadratically in a Sobolev space W. To overcome the crowding an elongated canonical region E should be chosen if the image region G is elongate...

The development of the plasma tail of comet Austin 1990 V on four consecutive CCD-images on May 6 1990 (Bonev & Jockers 1994) looks strikingly similar to the results of timedependent three-dimensional MHD calculations modeling the effect of a sudden rotation of the interplanetary magnetic field (IMF) by 90deg (Rauer et al. 1995). Assuming that the...

The effects of several types of tangential discontinuities in the solar wind on cometary plasma tails are studied using a time-dependent 3-D MHD model (Schmidt-Voigt 1989). First, a change in the solar wind direction by 6 deg has been simulated. This model shows a gradual turn of the plasma tail towards the new flow direction. A rotation of the int...

The response of a cometary plasma tail to interplanetary shocks is studied by means of time dependent three dimensional magnetohydrodynamic (MHD) model simulations. Three major phenomena are identified which can be seen by ground based observations. First, the plasma compressed by the shock forms tail rays. Secondly, the shock excites a transversal...

First from a one-dimensional MHD model we derive estimates for position and shape of the bow shock applicable for arbitrary magnetosonic Mach numbers greater than 1 in the solar wind. This generalization is important in the case of the Giotto encounter with P/Grigg-Skjellerup with the unusual interplanetary magnetic field (IMF) of 18 nT. We compare...

Cometary plasma flow was sampled by spacecraft along inclined trajectories through Comets Giacobini-Zinner and Halley. The interpretation of these observations needs extensive modeling of the whole comet. Here, some global simulations of cometary plasma flow are reviewed based mainly on MHD. Features from the first deceleration of the solar wind ou...

Coma science from the bow shock to the nucleus-coma interface and the formation of the plasma tail is reviewed. Departures from spherical symmetry caused by nucleus activity, distributed sources, UV flux, and radiation pressure are discussed. Gas and dust jets observed in the coma bear out the asymmetric gas production from a much lower percentage...

It is shown that for nearly circular regions discretized versions of the Newton type methods of Wegmann (1978) and Hübner (1986) converge locally to fixed points. Convergence is linear. The rates can be determined approximately for several standard regions. The dominant operator acts only on a subspace of high-order harmonics. Therefore under condi...

The functional analytic principle of alternating projections is used to construct an iterative method for numerical conformal mapping of the unit disc onto regions with smooth boundaries. The result is a simple method which requires in each iterative step only two complex Fourier transforms. Local convergence can be proved using a theorem of Ostrow...

Stationary MHD models are used to analyze the data of magnetic field measurements in comets Giacobini-Zinner and Halley. The contributions of the draping, of changes in the IMF, and of turbulence are separated and extended patches of unidirectional field regions are identified. A time-dependent MHD simulation of the nonstationary flow following a s...

Let G be a simply connected region with 0 ϵ G and with a twice Lipschitz continuously differentiable boundary curve, Γ, and let zμ, μ = 1,…, N, be an even number of N = 2n equidistant grid points on the unit circle {sfnczsfnc = 1} with z1 = 1. Then there exists for all sufficiently large N a polynomial P̂n of degree n + 1, normalized by the conditi...

This paper describes recent hydrodynamic and magnetohydrodynamic (MHD) simulations for the gas and plasma flow around a comet with detailed photo and chemical reaction network of 59 neutral and 76 ionized chemical species. The method allows for a separate energy balance of the electrons, separate flow of neutral gas, fast neutral atomic and molecul...

An MHD and chemical comet-coma model was developed, applying the computer program of Huebner (1985) for the detailed chemical evolution of a spherically expanding coma and the program of Schmidt and Wegman (1982) and Wegman (1987) for the MHD flow of plasma and magnetic field in a comet to the Giotto-mission data on the ion abundances measured by t...

An MHD and chemical comet coma model was applied to the plasma flow, the magnetic field, and the ion abundances in Comet Halley. By alternating iterations between axisymmetric models with detailed chemistry and three dimensional models with rigorous account of the Lorentz forces, a consistent description of the plasma flow and chemical evolution in...

Sublimation (vaporization) of the icy component of a cometary nucleus determines the initial composition of the coma gas as it streams outward and escapes. Photolytic reactions in the inner coma, escape of fast, light species such as atomic and molecular hydrogen, and solar wind interaction in the outer coma alter the chemical composition and the p...

Some improvements in the Schmidt-Wegmann numerical model of the interaction of the solar wind with a comet are reported. The generation of energy and ion mass by photoprocessses, electron impact, charge exchange, and recombination are shown and discussed, as are the total magnetic field, some field lines, mass density, and velocity in a cut-through...

It is shown that Fornberg’s method [1] is a discretized version of an iterative process which is essentially the same we introduced and studied in [7], [8]. The main difference consists in the determination of the shift $U_k $ in each iterative step. While we give an explicit representation of $U_k $, Fornberg determines $U_k $ from a linear equati...

A 3-dimensional MHD model for a Halley type comet is presented and compared with the magnetic field measurements of the Giotto spacecraft. The model takes into account the inclined interplanetary field, the net effect of mass loading by ionisation of the cometary gases, the elastic collisions between neutrals and ions, and the Lorentz-forces of the...

A computer model of Comet P/Giacobini‐Zinner is presented which contains photo‐processes, gas‐phase chemical kinetics, energy balance, multifluid hydrodynamics with a transition to free molecular flow, and solar wind interaction. Recently, the physics for electrons in the model has been improved by including electron impact ionization and dissociat...

An iterative method is described for the determination of the conformal mapping of a circular annulus Rq ≔ {z:q < |z| < 1} onto a doubly connected region G with smooth boundary curves. The method is analogous to the method of [7] for simply connected regions. It requires in each step the solution of a Riemann-Hilbert problem on Rq. This problem can...

The iterative method as introduced in [8] and [9] for the determination of the conformal mapping [(h)\dot] ¹ 0\dot \eta \ne 0 then the method converges locally in the Sobolev spaceW of 2-periodic absolutely continuous functions with square integrable derivative. If is in a Hlder classC 2+, the order of convergence is at least 1+. If is inC l+1+ wi...

Plasma flow and field amplification, resulting from the interaction of the solar wind with a comet, are studied by model calculations for the rates G = 7 X 10 to the 26 power to 2 X 10 to the 30 power of total cometary gas production. The influence of the magnetic field is investigated, using an axisymmetric model. A three-dimensional magnetohydrod...

We present in this paper a relatively simple method for the numerical solution of the MHD-equations on a curvilinear grid. We consider the full 3D equations as well as a modified axisymmetric version. The difference scheme is based on the principle of forming backward differences along characteristics in the spatial variables. This method is used t...

Water chemistry is central in understanding the physics and chemistry of cometary comae. Prior to the Deep Space 1 encounter with comet 19P/Borrelly, a rather advanced knowledge of water chemistry had been attained from studies of previous comets via ground-based observations and in situ spacecraft measurements, especially the Giotto encounter with...