Coathanger Cluster (CR 399)
July - Sept 2013
The Coathanger Cluster (Collinder 399) is not a true cluster.
More properly it should be regarded as an asterism
like the constellations. It is a collection of unrelated stars
that appear to form a pattern. The cluster is located in
This project was done using Narrowband
for Stars. This is a project to test using narrowband
techniques to capture objects that would normally be the subject of
LRGB. Since I my observatory is located within the tenth
largest city in the US, my sky is seriously light polluted.
For this project I used the Strömgren
V and Y filters combined with a broadband 20 nm H alpha
filter. For identification these are referred to as sV, sYel,
click for a full size (9"/pixel)
Note the red spot toward the lower left of the image. When I
first saw this I figured my Ha20 filter had introduced some
noise. Not so. Instead it increased the contrast of
hydrogen enough that a small Sharpless object was visible.
Cartes du Ciel
click for full size image
|600s x 13
|600s x 21
|600s x 28
Since the 3 filters produce something very different from RGB I
used G2V color calibration to balance the colors. HIP 96037
is relatively close to CR399. Using 30 second exposures I
measured the sV, sYel, and Ha20 filters to be ratios of .26:
1 : .68. Since Pix Color cal uses 1 as the weakest signal I
plugged in 1: .26 : .38 into the manual calibration.
From that point it was just normal processing. Since these
were just stars I chose to not aggressively stretch the final
image. TGVDenoise was the only other operation besides color
calibrations. Since the Ha20 filter captures the Hydrogen haze
of the Milky way I tuned down the red in the background.
Are the Colors Correct?
For this I refer to the the APOD by
Rogelio and this
image of the CoatHanger by Greg Noel. To my eye the colors look
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