The Multitude of Molecular Hydrogen Knots in the Helix Nebula
نویسندگان
چکیده
We present HST/NICMOS imaging of the H2 2.12 μm emission in 5 fields in the Helix Nebula ranging in radial distance from 250–450 from the central star. The images reveal arcuate structures with their apexes pointing towards the central star. These molecular hydrogen knots are most highly structured in the fields closest to the central star and become increasingly less structured with increasing radius. Comparison of these images with comparable resolution ground based images reveals that the molecular gas is more highly clumped than the ionized gas line tracers. From our images, we determine an average number density of knots in the molecular gas ranging from 162 knots/arcmin in the denser regions to 18 knots/arcmin in the lower density outer regions. The decreasing number
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