3D numerical simulations of radiative transfer in the cometary coma
0
Citation
0
Reference
20
Related Paper
Keywords:
Coma (optics)
Cite
A simple cometary outer ion coma model is constructed by adopting published results from numerical MHD computations. The ion composition and density distributions so derived are used to highlight some of the basic features of cometary plasma flows and the need for cometary ion observations with absolute brightness calibration.
Coma (optics)
Cite
Citations (0)
In order to understand the physical and chemical processes which produce the observed spatial morphology of the cometary coma, it is necessary to analyze observational data with physically meaningful models. Thus, a coupled program of theoretical modeling and complementary observational data analysis was undertaken regarding the spatial distributions of neutral gases in the coma. More, specifically, the particular topics of interest are: (1) the theoretical modeling of the nonequilibrium dynamics of the inner coma with emphasis on the region of the coma from the transition from collisional fluid flow out to the free-flow region and on observable conditions in the coma (i.e., density, outflow speed, and temperature); and (2) the model analysis of an important set of long-slit CCD spectra of comets. The side-by-side development of models along with the observation and analysis of data is an important and integral part of this project. The scientific community has in hand valuable observational and in situ data regarding one comet, Halley. It is important to use Halley as the benchmark by which other remotely observed comet data can be understood. Therefore, the self-consistant analysis of data with appropriate models is of the utmost importance. The data analysis work includes the analysis of the spatial profiles of (OI), NH2, CN, and C2.
Coma (optics)
Outflow
Cite
Citations (0)
Abstract In the stellar chromospheres, radiative energy transport is dominated by only the strongest spectral lines. For these lines, the approximation of local thermodynamic equilibrium (LTE) is known to be very inaccurate, and a state of equilibrium cannot be assumed in general. To calculate the radiative energy transport under these conditions, the population evolution equation must be evaluated explicitly, including all time-dependent terms. We develop a numerical method to solve the evolution equation for the atomic-level populations in a time-implicit way, keeping all time-dependent terms to first order. We show that the linear approximation of the time dependence of the populations can handle very large time steps without losing accuracy. We reproduce the benchmark solutions from earlier, well-established works in terms of non-LTE kinetic equilibrium solutions and typical ionization/recombination timescales in the solar chromosphere.
Chromosphere
Benchmark (surveying)
Cite
Citations (2)
Cite
Citations (2)
Numerical models
Cite
Citations (0)
Context. Cometary dust particles are subjected to various forces after being lifted off the nucleus. These forces define the dynamics of dust, trajectories, alignment, and fragmentation, which, in turn, have a significant effect on the particle distribution in the coma. Aims. We develop a numerical thermophysical model that is applicable to icy cometary dust to study the forces attributed to the sublimation of ice. Methods. We extended the recently introduced synoptic model for ice-free dust particles to ice-containing dust. We introduced an additional source term to the energy balance equation accounting for the heat of sublimation and condensation. We use the direct simulation Monte Carlo approach with the dusty gas model to solve the mass balance equation and the energy balance equation simultaneously. Results. The numerical tests show that the proposed method can be applied for dust particles covering the size range from tens of microns to centimeters with a moderate computational cost. We predict that for an assumed ice volume fraction of 0.05, particles with a radius, r >> 1 mm, at 1.35 AU, may disintegrate into mm-sized fragments due to internal pressure build-up. Particles with r < 1 cm lose their ice content within minutes. Hence, we expect that only particles with r > 1cm may demonstrate sustained sublimation and the resulting outgassing forces.
Sublimation
Outgassing
Cite
Citations (7)
view Abstract Citations (86) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Monte Carlo Particle Trajectory Models for Neutral Cometary Gases. I. Models and Equations Combi, M. R. ; Smyth, W. H. Abstract The Monte Carlo particle-trajectory models for the distributions of neutral gases in cometary atmospheres, developed in original form several years ago, have been greatly extended and generalized. In a Monte Carlo particle-trajectory model (MCPTM) the spatial distribution of a neutral cometary species is determined by calculating the explicit trajectories of many individual particles following the chain of parent vaporization, coma outflow, photodissociations, collisions, and decay through the appropriate number of generations. In this paper the mathematical derivations of the various methods employed in the MCPTM are presented in detail, and the application of the MCPTM to the calculation of the photochemical heating of the inner coma through the partial thermalization of cometary hydrogen atoms produced by the photodissociation of water is discussed. Publication: The Astrophysical Journal Pub Date: April 1988 DOI: 10.1086/166260 Bibcode: 1988ApJ...327.1026C Keywords: Comet Tails; Cosmic Gases; Mathematical Models; Monte Carlo Method; Particle Trajectories; Stellar Atmospheres; Computational Astrophysics; Particle Acceleration; Radiation Pressure; Solar Radiation; Time Dependence; COMETS; MONTE CARLO METHODS; PARTICLES; TRAJECTORIES; NEUTRAL PARTICLES; GASES; MODELS; CALCULATIONS; NUMERICAL METHODS; DISTRIBUTION; ENERGY; ATMOSPHERE; COMAE; PARAMETERS; RADIATION; PRESSURE; EJECTION; VELOCITY; TEMPERATURE; TIME DEPENDENCY; PHOTOCHEMISTRY; HEATING; GEOMETRY; ACCELERATION; DIAGRAMS; Astrophysics; Comets; COMETS; PARTICLE ACCELERATION full text sources ADS | Related Materials (1) Part 2: 1988ApJ...327.1044C
Radiation Pressure
Particle (ecology)
Cite
Citations (76)
Numerical models
Cite
Citations (0)
Inviscid flow
Cite
Citations (3)