H2O(+) ions in the inner plasma tail of Comet Austin 1990 V

Details H2O(+) ions in the inner plasma tail of Comet Austin 1990 V H2O(+) ions in the inner plasma tail of Comet Austin 1990 V

Feb 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994icar..107..335b&link_type=abstract

Icarus, vol. 107, no. 2, p. 335-357

Computer Science

21

Absorption Spectra, Austin Comet, Comet Tails, Cosmic Dust, Emission Spectra, Ion Density (Concentration), Water, Continuums, Fabry-Perot Interferometers, Image Analysis, Photoionization, Spectrum Analysis, Comets, Austin, Water, Ions, Plasma, 1990V, Emissions, Ccd Methods, Earth-Based Observations, Interferometry, Distribution, Comet Nuclei, Comae, Density, Symmetry, Gradients, Comet Tails, Mass Loading, Abundance, Model, Production Rate, Velocity, Comparison, Analysis, Data Reduction, Calculations, Morpho

Scientific paper

Narrow-band images of Comet Austin 1990 V in the light of the red (0-8-O) H2O(+) emission (6199 A) are presented. The observations were carried out in the period April 30-May 7, 1990, with a focal reducer, Fabry-Perot interferometer, and a charge coupled device (CCD) camera attached to the 1-m telescope of Hoher List Observatory. The high spectral resolution of the images allowed a precise subtraction of the dust continuum even at the nucleus and a reliable absolute calibration. Thus, for the first time, the spatial distribution of water ions and its temporal behavior is observed in the cometary coma including the area close to the nucleus. Peak column densities between 1011 and 2 x 1011/sq cm were obtained in the observational period. Close to the nucleus the column density distribution is strongly asymmetric. Toward the Sun the column density gradient is steep. In this direction the column density decreases by a factor of approximately = 4 over a distance of 104 km. In the tailward direction the distribution is flat. Frequently the column density maximum is shifted tailward. The contour passing through the nucleus usually extends more than 104 km tailward. This is caused by the mass loading of new ions into the tailward cometary plasma flow. We have integrated the column densities perpendicular to the tail direction and calculated the number of water ions per unit tail length. The derived profiles always have their maximum significantly shifted tailward. They are compared with a simple model of H2O(+) production by photoionization of water. Good qualitative agreement is obtained but the mean ion velocities deduced from the model are too high by about a factor of 10. Probably a significant part of the ions in the flanks of the tail is not detected in our observations. The time interval of 22-23 min between successive images allows to study turns of the plasma tail and the formation of ray structures near the cometary nucleus.

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