Cometary knots in the Helix Nebula
Handron, Kerry Dorinda Patrick
O'Dell, C. Robert
Master of Science thesis
The central star of the Helix Nebula, the closest planetary nebula, is ringed by hundreds of Cometary Knots. Presented here are images taken with WFPC2 of a field in the northern portion of the bright ring and some physical parameters and models derived from the data. The field of view contains more than thirty well formed Cometary Knots and reveals that the entire bright ring is composed of knot-like structures. The data is in three narrow emission line filters, H$\alpha$, (OIII) and (NII). Optical thickness to ionizing photons for the knots is established, physical properties such as density in the ionized portions of the knots and dust mass are determined and the beginning of a model to explain the detailed structure set forth.