Despite my return to galaxies last post I'm not done with planetary
nebula. NGC 7094 a planetary in Pegasus not far from the famous
globular cluster M15. The central star in this nebula is a rather odd
star. It is known as a hybrid PG 1159 star. What this means is that
it, first off, has an unusual amount of hydrogen left in its atmosphere.
Secondly it is a variable star. White dwarf stars are normally dead
stars only giving off heat and light stored in them when their nuclear
furnaces were still working. When they die they throw off the outer
atmosphere that still has hydrogen, creating the planetary nebula, and
retaining the core of heavier elements created by the nuclear furnace.
They get a small amount of energy from gravitational collapse as they
cool but they shouldn't very in brightness. But some do. It is thought
that the outer atmosphere of the star becomes more or less opaque
depending on the ionization level of certain heavy elements such as iron
in the atmosphere. It is this variation of ionization that makes the
star appear to vary in brightness. In fact it doesn't, its just that
the atmosphere blocks the light at time. Such cycles are very
irregular. In this case the star varies at a rate of 2000 to 5000
seconds. Since my exposure of this guy was 6000 seconds it may have
varied 3 times during my exposure! Thus catching this isn't easy, nor
would I try. I knew this before I took the image.

What I didn't know was that it shares the field with a very faint
nebulosity. This nebulosity isn't listed in any catalog I have, nor
does it appear to be galactic cirrus. Not expecting it I severely
underexposed for it, especially the color frames which are very noisy.
Don't consider the color of this faint nebulosity as at all correct, the
color is mostly noise. If anyone knows what it is please let me know.
I need to go back and try a much longer exposure. But something is
reflecting into my field. When I centered the nebula a rather bright
ghostly nebula appeared to the west of the nebula. I have no idea where
the reflection came from, M15? To get rid of it I had to lower the
object. Raising it didn't help. Since the nebula is mostly "below" the
planetary that means I lost some of it, though I didn't realize it at
the time. I can't find any reliable distance data for this planetary.
Again, if anyone knows let me know.

Conditions went from fair to bad during this exposure. The loss of
resolution caused the blue and especially green frames to be "defocused"
creating the odd blue-green halos around bright stars as well as making
them larger than usual. Yet another reason to redo this one but I have
such a backlog of objects not taken the first time it is hard to go back
and reimage those I should.

14" LX200R @ f/10, L=4x10', RGB 2x10' binned 3x3, STL-11000XM, Paramount ME.

Rick

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Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

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