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NGC 7789 (Caroline's Rose) with a QHY5III-178C

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#1 james7ca

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Posted 11 September 2019 - 07:56 AM

This is a notable star cluster in Cassiopeia that is missing from the Messier catalogue. The brightest members of this cluster are highly evolved orange giant stars and the cluster itself is quite old for an object of this type.

 

This seems to be a popular target for visual observation and it is one of the few deep space objects in Cassiopeia that shows up clearly in wide-field, broad-band images of this region. Some of the other candidates are the Owl Cluster (NGC 457), the Double Cluster, M103, the Pacman Nebula, and to a lesser extent the Heart and Soul Nebulae (the latter better in deeper narrow-band images). See my next post for a shot of the Cassiopeia area taken with a 35mm lens and a Nikon D5100.

 

The image was taken with an uncooled QHY5III-178C camera (just under one hour of total integration time, 707 x 5s, gain zero) using a Stellarvue SV80ST2 scope with a 0.8X Stellarvue reducer all carried unguided on a Celestron AVX mount. Image capture using SharpCap, image processing with PixInsight and Photoshop CC2019.

 

I'm not completely happy with this result, since I think it would be better to use a longer exposure setting than 5 seconds to capture the fainter members of the cluster. Also, the framing is a little too tight, it would be better to have a wider field and perhaps next time I will use my ASI183MM camera on a guided mount. Lastly, it was hard to get a good JPEG compression result on this given the 500KB limit here on CN. Or, those are among my excuses for any shortcomings. wink.gif

 

However, I do think this serves as a decent example of what can be done with a relatively inexpensive, uncooled CMOS camera using short, unguided exposures on a relatively low-end mount and all done rather quickly under red/orange zone light pollution. That said, the Stellarvue scope is no slouch although the 0.8X reducer was never that great (since discontinued by Stellarvue, perhaps for cause).

 

C&C welcomed. 

Attached Thumbnails

  • Caroline's Rose with QHY5III-178C (Small).jpg

Edited by james7ca, 11 September 2019 - 08:24 AM.

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#2 james7ca

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Posted 11 September 2019 - 08:01 AM

Here is a locator image that was taken with a 35mm Nikkor AI-S lens at f/5.6 on a Nikon D5100. Captured unguided on an AVX mount with 115 minutes of integration time (230 x 30s, ISO800) under red/orange zone light pollution.

 

Image processing with PixInsight (including annotation) and Photoshop CC2019 (including further annotations).

Attached Thumbnails

  • Cassiopeia (Small).jpg

Edited by james7ca, 11 September 2019 - 08:11 AM.

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#3 PirateMike

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Posted 11 September 2019 - 08:36 AM

That is a spectacular image, the colors are fantastic. bow.gif

 

 

Miguel   8-)

 

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#4 petert913

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Posted 11 September 2019 - 09:24 AM

NGC7789 is a new one on me.  And I can't wait to check it out !



#5 james7ca

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Posted 11 September 2019 - 11:17 AM

Miguel and Peter, thanks for the notice.

 

Just out of curiosity I went over to WikiSky.org to see if I could determine the limiting magnitude in my image. It was pretty easy to find stars in the image that were listed by the Palomar Digitized Sky Survey II as being around magnitude 17.5 and the faintest stars are somewhere between that value and where WikiSky stops reporting values, which I think is around magnitude 18.

 

Then I did a crop of the area that is on the right side of the cluster to compare my image to the sky survey (shown below). The images that were used for the Palomar survey (DSS II) were based upon photographic plates recorded between 1987 and 1998 using Palomar's 48 inch Schmidt camera. I'm not sure what exposure times were used for the DSS II survey, but the preceding DSS I survey used exposures that ranged from 40 to 70 minutes (on very large format photographic plates).

 

On the DSS II the limiting magnitude for the red channel was 20.8 and that for the blue was 22.5 and so the sky survey image is probably about two to four magnitudes below what I recorded. The colors look pretty close, but the DSS II survey was based upon red, blue, and near IR plates so I don't think I should use those images as an absolute color reference. However, some of the more well know objects that are shown in the DSS II look pretty "normal" in terms of color, so the images on WikiSky can't be that far from correct. That said, my stars look just about as small as in the survey, although the survey plates were scanned at around 1 arc second per pixel whereas my original capture scale was near to 1.3 arc seconds per pixel. However, in this comparison both samples have been reduce in size by about 50% (to around 2.4 arc seconds per pixel).

Attached Thumbnails

  • DSS II Comparison.jpg

Edited by james7ca, 11 September 2019 - 12:01 PM.

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