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Open Cluster NGC 6823 and Emission Nebula Sharpless 86 in Hydrogen Alpha Light

NGC 6823 and Sharpless 86 are an interesting open cluster and emission nebula combination in the constellation of Vulpecula.  The open cluster NGC 6823 is believed to be about 2 million years old  and is believed to be about 6200 light years away.  The intense radiation of the large and bright stars of the cluster are believed to be eroding away the surrounding dust and gas and are the source of the light emitted by Sharpless 86.  An interesting feature of Sharpless 86 is the large “elephant trunk” structure seen just to the left of the cluster which is being eroded away by the radiation of the stars of NGC 6823.

This image was taken on June 18, 2018 at the San Diego Astronomy Association site at Tierra del Sol, California with a Stellarvue SV70T and the dedicated f/4.8 reducer/flattener.  The camera was a ZWO ASI1600MM-Cooled camera using a Baader 7nm 36mm hydrogen alpha filter.  The camera gain was set to 200, the offset was 50, and the camera was cooled to -5 and to -15 C..  I took 33 sub-exposures of 270 seconds each.

There were several “challenges” with getting the sub-exposures for this image.  First, my image acquisition program, Sequence Generator Pro, locked up because it was connected to my mount when I reinitialized the mount after it stalled for some reason.  I turned the camera cooling back on when I re-started the program but I didn’t notice that I had the temperature set to -5 instead of -15 until I had taken 23 exposures.  Second, the relative humidity at Tierra del Sol was 98%  that night, and although I had dew heaters running on my imaging and guiding scope, I didn’t have them on high enough for the conditions.  After I stopped the imaging run I saw that the imaging scope had a light coat of dew on the objective lens.  So, I lost more than an hour of subexposures at the end of the imaging run.

Processing Details:  Image calibration, alignment and stacking was performed with PixInsight.  PixInsight’s fantastic DrizzleIntegration tool was also used in the image stacking process.  I used a light application of MultiscaleLinearTransform to attenuate noise in the image.  A moderate histogram stretch was performed.

The image below is a high resolution center crop highlighting the elephant trunk and the open cluster.  Click on the image below to see a larger view.  Click on this link to see a 3000 x 3000 pixel high resolution version.

The image below is a full frame wide field view of the area surrounding Sh2-86.  Click on the image below to see a larger view.  Click on this link to see the wide field image at the camera’s native resolution (4656 x 3520 pixels).

Posted in Bright Nebula, Processing Notes, Star Clusters

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