ASTRO: Sh2-68

PK 030+06.1 is a planetary nebula better known as Sh2-68 in Serpens
Cauda. It is "A Planetary Nebula Leaving it's Mark on the Interstellar
Medium" as one paper on it is entitled. Hey, a paper without some
stodgy title for a change.
http://adsabs.harvard.edu/full/2003IAUS..209..525K . According to the
paper and other sources its distance is still undetermined.

It is a very old planetary, at least 45,000 years old according to the
above paper. It's expansion and movement through space has been halted
by the InterStellar Medium (ISM). Now the nebula is moving with the ISM
and no longer following the motion of the central star. This is why it
is found off center to the southwest. The nebula has been moving
through the ISM for at least 45,000 years and leaving a tail of stripped
material behind. Some of this is seen in very deep narrow band images.
Being a contrarian I decided to see what I could pick up using LRGB
only from my very dark location. I put the nebula low in case I picked
up the tail running up and to the left. Turned out my sky that night
had severe sky glow which drown out any attempt at picking up the tail,
at least with only 40 minutes exposure time. The off center, very blue
(somewhat cyan), central star stands out against the mostly dust
reddened background stars. All those dust reddened stars show the
density of the ISM it is passing through. The nebula's prior expansion
and now cooling central star means it gets somewhat less ionizing
radiation than a young small planetary which results in its faintness.
It appears the ISM is putting more drag on the smaller and lighter
ionized hydrogen atoms than the OIII as most of the red of the ionized
hydrogen is found behind the blue OIII regions. This is far more
obvious in narrow band images however. I do need to revisit this one
sometime with narrow band filters.

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

Rick
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