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B. Komitov (Institute of Astronomy - Bulgarian Academy of Sciences), B. Bonev (Bowling Green State University)
We developed two-factor regression models for the scale lengths of CN and its parent molecules with respect to the heliocentric distance and the level of solar activity, represented by the 10.7-cm solar radio flux. The choice of this particular index of solar activity is based on its correlation with the level of the solar UV radiation. The data for the CN parent scale length include 72 reported values from various comets during the period 1970-1990. The data for the CN scale lengths include 22 values for the period 1985-1990. The model for the parent scale length is obtained for heliocentric distances between 0.44 AU and 2.68 AU. The model for the CN scale length - for heliocentric distances between 0.64 AU and 1.66 AU. Although the heliocentric distance is the main factor, the solar activity influence on the scale lengths is very significant. The observed values for the CN parent at 1 AU differ about 3-4 times between minimum and maximum of the 11-year cycle. This effect is demonstrated with examples from observations of the comets Halley (1986), Austin (1990) and Levy (1990). In spite of using data from various comets and from different observers, the two regression models show that more than 85% of the variations in the scale length values may be explained with variations of the heliocentric distance and the level of solar activity. We acknowledge the assistance of Dr. Grayzeck, from the University of Maryland, who provided us with the International Halley Watch CD-ROM archive.
The author(s) of this abstract have provided an email address for comments about the abstract: komitov@mbox.digsys.bg