Comet Hale - Bopp Near Nuclear Research

The cometary study is reviewed briefly in this presentation. The recent results of Comet Hale-Bopp, (e.g. dust and gas production rate, size distribution of cometary dust, expanding velocities of dust and gas, spin period of nucleus, orientation of spin axis, outburst of inner coma, and cometary X-ray emission) are summarized here. The light curve and images of C/ 1995 Olin September 1996 are studied. It is found that an outburst happened on 10-11 September 1996. The magnitude of the inner coma region increased by 2.1 and 1.4 mag on these two days, respectively. Two globular ejecta were found near the nucleus of the comet on 10-11 September 1996. By extrapolating backward from the ejecta, it is found that the initial time of the outburst was on 9 September (9.5 ?0.2 UT). The physical reason for this outburst is still uncertain. The projected radial velocities of ejecta are 120 and 97 mIs. Owens et al (1998) found X-ray emission of this comet during that period. In this paper, Wavelet Analysis is brought into use to process the CCD images of Comet Hale-Bopp, which were obtained with the 1.56 m telescope of Shanghai Astronomical Observatory. This method depresses the coma background and enhances the features of coma. It is possible for us to measure the ejection velocities (EVs) of jets on different days. According to the reported rotation period of Comet Hale-Bopp, which is about 12 hours, the average EV of the jets is determined to be (599?4) m/s based on 27 measurements. In addition, it is discovered that the velocity is different for each jet and for each different day, with a variation ranging from 200 to 900mIs. We present a simulation based on the morphology of the inner coma of Comet Hale-Bopp obtained early in 1997, when the features of coma varied dramatically. The simulation is based on spin stable. Two active regions are suggested by the coma morphology. The dust grains are ejected from the rotating nucleus and subjected to the solar radiation pressure. The trajectories are projected on the sky plane and then they are compared to the observation data. The synthetic images can fit the observations well. The results show the spin mode is a simple one. The precession component, if it exists, may be very small. The RA and Dec of the pole of rotation, are 250 and -60 degree respectively. The latitudes of the two active sources are 0 and 30 degree9 respectively. The rotation was stable during that period. The coma morphology can be interpreted by the model with one nucleus and two active regions. The two-nuclei model is not necessary to be introduced.