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Session 75 - The Crab Nebula.
Display session, Thursday, June 13
The Crab filaments consist of gas photoionized by the radiation of the synchrotron nebula and hence are seen in emission lines. Recent HST-WFPC2 observations of the northern part of the nebula taken through several narrow line filters show a wealth of structure. The filamentary structure is a result of magnetic R-T instabilities at the interface between the synchrotron nebula and a swept up shell of ejecta (Hester et al, 1995, ApJ 456,225). Variations in the densities and magnetic fields at the interface produce a range of filament types, distinguishable by their ionization structure. We isolate individual filaments of different types and obtain their shapes and brightnesses. We then match these filament properties with photoionization models calculated using CLOUDY (Ferland, 1993, Univ. of Kentucky Department of Physics and Astronomy Internal Report). The model results, which are calculated in one dimension are converted to quasi two dimensional models assuming cylindrical geometry for the filaments. We obtain the range of observed filament properties by varying our model input parameters and examine the effect these variations have on a number of predicted line strengths and line ratios.
Program listing for Thursday