Analysis of the Swings effect and Greenstein effect in comet P/Halley
Date
1988
Authors
Jaworski, Wayne Anthony
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Abstract
Spectra have been obtained of Comet P/Halley using the Image Photon Counting System (IPCS) on the Anglo-Australian Telescope in April 1986 by Dr. J.B. Tatum. The CN (0,0) violet system is analyzed to demonstrate the Swings resonance-fluorescence mechanism and multiple spectral images are used in creating a velocity map of the CN gas throughout the coma by application of the Greenstein effect. A new method for solving Abel's equation is developed and tested. This method is applied to a surface density profile of Comet IRAS-Araki-Alcock in order to recover the space density profile through the coma of this comet. The resultant profile is incorporated into theoretical models of the Greenstein effect.
The theoretical calculations of the Swings effect are found to be in good agreement with the observed intensities of the R-branch lines of Comet P/Halley. This validates the assertion of an optically thin coma. In addition, 13 lines interspersed throughout the R-branch are identified as lines belonging to the CN (1,1) band system and the 13CN (0,0) band system. The 13CN (0,0) isotope R(7) and R(8) lines are used to obtain the 12C/13C ratio in the comet. A value of 88.9 ± 1.8 is found in agreement with the solar value and past determinations with other comets. The Greenstein effect is seen observationally and velocity profiles through the coma are obtained by modeling the R(9)/R(12) ratio of the CN (0,0) band. Changes in radial velocity as large as 1.57 km/s are found to exist within spatial distances of 4,500 km. Theoretical models of the Greenstein effect show that gas jets emanating from the rotating nucleus can account for much of the observed complexity.