Statistics – Computation
Scientific paper
Aug 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994p%26ss...42..643o&link_type=abstract
Planetary and Space Science (ISSN 0032-0633), vol. 42, no. 8, p. 643-649
Statistics
Computation
12
Comets, Computational Astrophysics, Cosmic Dust, Infrared Astronomy, Magnetite, Mathematical Models, Olivine, Silicates, Spectrum Analysis, Stellar Models, Fractals, Functions (Mathematics), Grain Size, Infrared Spectra, Mixing Ratios, Spectral Signatures, Thermal Emission
Scientific paper
Thermal emission from cometary dust grains has been examined using model calculations of aggregates with fractal structure consisting of two components, namely silicate (olivine) and absorbing material (magnetite). Calculations of the thermal emission have been performed by using the discrete dipole approximation for small aggregates, and Mie theory with the Maxwell-Garnett rule for large aggregates. We have used the size distribution of the aggregates converted from the mass distrubution of grains detected in comet P/Halley taking into account the fractal aggregate model for cometary grains. It is found that the spectral feature at about 10 micron wavelength is mainly controlled by a fractal dimension D of the aggregates, whereas the temperature of the aggregate strongly depends on a mixing volume ratio M of magnetite to a whole volume, i.e. M = (magnetite/olivine+magnetite)). When the cometary dust grains consist of the fractal aggregates with D approximately equal to 2 and M = 0.15, a remarkable twin-peaked structure in the 10 micron silicate band appears even when large aggregates contribute to the infrared spectral feature. We conclude that the model calculations support an interpretation of the observational data in terms of porous particles consisting of different materials.
Kozasa Takashi
Mukai Tadashi
Okamoto Hajime
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