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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 Vulpecula.

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, and Ha20.

CR 399
                Coathanger cluster using NB4Stars (sV,sYel,Ha20)
click for a full size (9"/pixel) image

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.

Annotated Map

Overview Map of CR 399
Cartes du Ciel

Annotated Map of CR399
click for full size image

Processing Details

Strömgren sV
600s x 13
Strömgren sYel
600s x 21
600s x 28

Color Calibration

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 the same.

Copyrights for Photos

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Except as noted, all work on this site by Robert J. Hawley is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. This permits the non commercial use of the material on this site, either in whole or in part, in other works provided that I am credited for the work.