Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........16s&link_type=abstract
Ph.D. Thesis Maryland Univ., College Park.
Astronomy and Astrophysics
Astronomy
2
Astronomical Models, Comets, Dust, Astronomical Photometry, Comet Nuclei, Cyanogen, Gas Composition, Halley'S Comet, Outgassing, Rotation, Time Dependence
Scientific paper
I have developed a time-dependent model to recover the production rate of a comet's outgassing species (molecules and dust) as a function of time from a series of photometric observations. The model has been applied to Comet Levy (1990c) to derive its dust production rate. Comparison of the dust production rate with spectroscopic data suggests that gaseous species must have a different temporal behavior from that of dust and is indicative of chemical heterogeneity of the nucleus of Comet Levy. I demonstrate using numerical simulations, that it is possible for CN jets seen in Comet P/Halley to evolve into CN shells as suggested by Schulz and Schlosser (1990). In indeed, this is the formation process of CN shells, the ejection velocity of CN in its precursor frame has to be much less than the outflow velocity of the precursors themselves. This rules out the canonical gaseous species as the precursor of CN radicals in CN jets and shells while favoring an origin in grains. In order to construct detailed models of the gaseous jets observed in Comet P/Halley, information about the rotational state of the nucleus is required. I have carried out an extensive search to determine all rotational state of Comet P/Halley which are capable of explaining a wide variety of observational data. I find that the orientation of the large end of the long axis during the Vega-1 encounter must be reversed from that suggested by Sagdeev et al. (1989) in order to satisfy some of the constraints. Neither pure rotations nor Short-Axis Modes are capable of satisfying the constraints. The most likely solutions are Long-Axis Modes. In the most likely modes for the rotational state, the long axis executes a precessional motion around the space-fixed total rotational angular momentum vector with a period near 3.7 days while performing a rotational motion around itself with a period of about 7.3 days. The direction of the total rotational angular momentum implies prograde rotation, but the exact coordinates are not well determined.
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