ASTRO: Sh2-165

Sh2-165 is a rather faint emission nebula Cassiopeia 1.75 degrees east
of M52. It is likely part of the Cas OB5 supershell. I found three
different distance measurements: 1.6±.5kpc, 1.9±.4kpc and simply 1.7kpc.
In light-years that's 5,200±1,600; 6,200±1,300 and 5,500 light-years
respectively. So say between 5000 and 6000 light years wouldn't be too
far off. Distances to such objects is not easy to determine. It's
surprising three different methods agreed so well. The one reference to
its illuminating star says it is a B0.5V star but didn't give a
position. I assume it is the bright one at the core but sometimes this
isn't correct. While it is blue it doesn't seem as blue as I'd expect
for a main sequence early B giant star.

I find very few amateur images of this one. Only one I found was Dan
Crowson's image which I apparently missed when he posted it, taken on
Sept 7, 2012. It gives a better feel for how faint this one is.
http://www.flickr.com/photos/dcrowson/7951182598/
Interestingly my image straddles his. Due to my poor skies and my
system that normally only images within 2 hours of the meridian I needed
several nights to get my 2.5 hours of data. My first frame was taken
August 26 and last September 13. It could have used more but after many
tries during that period I apparently decided to move on. While I did
take some luminance data the Milky Way stars so dominated those frames I
decided to only use the H alpha frames for the starfield as well as
nebula as otherwise it would have been swamped by the stars. So the
starfield was done solely from the RGB data and the nebula from a mix of
RGB and Ha in which the red channel used 75% of the Ha data and the blue
channel 20% to simulate H beta. This left the nebula rather magenta so
5% H alpha was added to the green channel to correct for that and
probably simulate what little OIII this object emits.

14" LX200R @ f/10, Ha=3x30' RGB=2x10', STL-11000XM, Paramount ME

Rick
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