Sunday, October 25, 2015

planetary nebula primer III, morphology

Planetary nebula can come in a variety of shapes.  Here are more old images demonstrating morphology.  Although relatively rare, some are nearly perfect spheres, the undisturbed exhalation of a dying star:

Abell 39:
Abell 34 "oozes faintness":
note the tiny background galaxy superimposed at the bottom edge

Most have more complex shapes.  The reason for the unusual shapes is not well understood.  Theories include interactions between the ejected gas layers, magnetic fields, planetary systems, and binary stars. 

Minkowski's Butterfly is thought to have a binary star orbiting
the white dwarf causing the central constriction with jets above
and below:

Here are a few classic bright-round-things-about-the-size-of-a-planet:

Cat Eye
Ghost of Jupiter

Clown Nebula
Blinking Planetary

Often there are faint outer layers evident on longer exposure reflecting multiple episodes of the central star shedding outer layers:
Cat eye
Blinking Planetary

Many are bipolar structures with a ring-like central constriction.  M 76 and M 57  are an example of two sides of the same coin.  

M 76 the little dumbbell left               M 57  the ring nebula right
side view of a ring                                     face on view of a ring
M57 (right) shows a bright ring with a very faint outer shell.  
Rotate that 90 degrees and you've got M76 (left) with the side view of the bright central ring appearing as a rectangle and the faint outer ring revealed as expansions blowing out on either side of the ring. 

Some have pairs of jets, ejecting material, typified by the saturn nebula:
Saturn Nebula

The jets are classically called ansae (wings), either way they are flying things.

Some of the jets have low energy NII regions at the tip aptly known by the acronym FLIERS 
(Fast Low-Ionization Emission Regions) which are more evident when a red NII filter is used:
Saturn Nebula red NII FLIERS

Blinking Planetary red NII FLIERS
IC2149, the Easter Egg Nebula
FLIERS appear to be relatively young, moving outwards at supersonic speeds.  Though poorly understood, the colorful wingtips make for nice images.
IC 4593 White-Eyed-Pea
IC 4593 displays many of the properties above and then some:

-small bright planetary

-faint outer core

-bipolar jets


-BONUS: the outer core is deformed by interaction with interstellar medium generating a bow wave upper right

More planetary nebula images here

A more scientific account of the modern concepts in planetary
nebulae morphology:

Shape, structure, and morphology in planetary nebulae

Richard A. Shaw

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