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Astrophotography by Bob Franke

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NGC 7686 - Cluster

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Click the image for ~ 55% size view. (2100 x 1400 - 1.08 MB)

Instrument

12.5" RCOS @ ~ f/9 (2880 mm fl) at 0.64 arcsec/pixel. Shown at  1.15 & 3.22 arcsec/pixel.

Mount

Paramount ME

Camera

SBIG STL-11000 w/ FW8 filter wheel & AstroDon Gen-2 RGB filters.

Acquisition Data

10/5/2017 to 10/8/2015 Chino Valley, AZ. with CCD Commander & CCDSoft.  AOL guided

Exposure

RGB

480 min (32 x 5 min. each) Bin 1x1

eXcalibrator RGB ratios are 1.00, 1.05 & 1.20

Software & Processing Notes

 

  • CCDSoft, CCDStack, PixInsight, Photoshop CS6.

  • eXcalibrator v6.1 for (g:r),(b:r) color balancing, using 360 stars from the SDSS-DR9 database.

  • CCDBand-Aid to repair KAI-11000M vertical bars.

  • CCDStack to calibrate the sub exposures.

  • PixInsight to register, data  reject, mean combine the sub exposures, create the RGB image, gradient removal, non-linear stretching with HistogramTransformation, color saturation and green cast removal with SCNR.

  • PhotoShop for additional background neutralization and JPEG creation. 

Comment

 

Shown rotated 155 clockwise.

NGC 7686 is cataloged as an open cluster in the constellation Andromeda. It is described as poorly populated with 50 to 80 stars. Distance estimates range from 900 to 3000 light years. William Herschel discovered it on December 3, 1787.

Since its discovery, like Pluto, astronomers later demoted NGC 7686. In 1961, Johnson et al. determined that it is not a cluster. Here is the text from their presentation in the Lowell Observatory Bulletin No. 113.

"Our color-magnitude diagram shows merely a uniform scatter with no significant tendency to show a cluster main sequence; we conclude that NGC 7686 is not a cluster."