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Abstract

We report continued detailed spectroscopic studies of highly articulated structures, called 'microstructures', in NGC 6543, 6826, and 7009. Of particular interest of these planetary nebulae (PNs) are FLIERs (fast, low-ionization emission regions) characterized by the following: ionization: much lower ionization than immediately adjacent gas; size: small size in at least one dimension (approx. = 2 sec, or about 0.01 pc at a distance of 1 kpc); morphology: generally ansae, jets, knots, or strings of knots; distribution: pairs (or sets of pairs) on equal and opposite sides of the central nucleus located near a nebular symmetry axis; velocity: each partner has equal and opposite highly supersonic velocity (approx. +/- 50 km/s); kinematic age: the kinematic age (projected distance/redshift) of some FLIERs is less than that of the rest of the PN; N abundance: apparent enhancement of nitrogen (only) relative to hydrogen by factors of 2-5; kinematic/thermal energy density: much higher kinetic energy per mass than thermal energy; and mass: typically 10-4 to 10-5 solar masses, and yet FLIERs exhibit little difference in density or temperature from their surroundings. These properties and their small kinematic ages lead one to expect that FLIERs are high-density, opaque (i.e., partly neutral), and highly collimated material expelled recently from the nucleus. Their high ram pressure (10 times greater than the thermal pressure of the confining gas) should lead to the formation of bow shocks. Contrary to intuitive expectations, however, most FLIERs show the ionization structure expected of bow shocks. No simple model accounts naturally for the observed properties of FLIERs.

FLIERs and other microstructures in planetary nebulae, 2

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Abstract

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