DPS 2001 meeting, November 2001
Session 20. Comet Posters
Displayed, 9:00am Tuesday - 3:00pm Saturday, Highlighted, Wednesday, November 28, 2001, 10:30am-12:30pm, French Market Exhibit Hall

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[20.07] CCD Imaging Observations of the Comae of Nucleus Fragments of the Splitted Comet Evans-Drinkwater (C/1996 J1)

I. Toth (Konkoly Observatory, Budapest)

The double nuclei of the nontidally splitted dynamically new comet Evans-Drinkwater (C/1996 J1) were observed from August 5 to October 14, 1997 in the 285 - 355 days interval after the breakup event determined by Sekanina (1998). CCD imaging photometric observations were made in the Cousins BV(RI)c photometric system at the Piszkesteto branch mountain station of Konkoly Observatory, Hungary. Wright Instr. Ltd. EEV CCD05-20 MPP (UV coated) detector was attached to the Cassegrain focus of the 1 metre Ritchey-Chretien-Coude (RCC) telescope. The high signal to noise ratio R and I filtered images were used to study the comae of the nucleus fragments A (the fainter one) and B (the brighter leading component). The isophote coma contours of the component B show a tailward (slightly deviated from the antisunward direction) and a smaller sun-directed dust emission features. Syndyne curves were generated for the dates of the observations and found that the maximum elongation of isophotes (``bulge") of the coma of B component precisely corresponds to the projected dust tail with low values of the radiation pressure parameter (with \beta~0.001). Finson-Probstein (1968) analysis was performed for the dates of the observations by adopting and modifying a model by Keller and Meier (1976) to the case of a single dust grain size. This simple approach demonstrates that a simple model of isotropic emission of dust subjected to radiation pressure is able to produce an elongated coma and its apparent orientation as observed. The maximum elongation of the tailward isophotes (the "axis" of the bulge) of the B component corresponds to the low values of the radiation pressure parameter (\beta) of the dust. The radial variations of the brightness in the coma were also analysed. The components were not strictly in steady state: deviations from the steady state brightness decreasing law, as steepening are observed. The steepening may be either due to the radiation pressure or fading grains. This comet was observed at low solar phase angles (less than 18.2\circ). For a comet observed at small phase angles, i.e., head-on, the apex distance (approximately less than ten thousand km) is not really relevant but it does indicate that radiation pressure cannot be effective alone to produce the steepening of the profiles beyond this distance. Grain fading as already proposed appears a plausible mechanism.

This work was supported partially by the Hungarian Research Foundation grants OTKA Nos. TO14963 and T025049. The author also acknowledges the special support from the CNRS, France.

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