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Hi
I was looking at this DSS image of the ACO2151 Hercules cluster of galaxies. Is the somewhat elongated faint, ring-like structure just north of the core a giant planetary nebula, or just an optical defect? It must be the latter, right?
http://pw2.netcom.com/~ahighe/A2151_60_60F.jpg
Clear Skies
Regards
Akarsh
Hi Akarsh,
Take a look at a picture of the area directly from the DSS site: https://archive.stsci.edu/cgi-bin/dss_form
It's an artefact that manifests itself on two older DSS images, taken minutes apart in the year 1950.
Go here http://archive.stsci.edu/cgi-bin/dss_plate_finder, enter the approximate J2000.0 coordinate of 16 04 36 +17 57 00, set 60 for both height & width, choose GIF or JPEG format and select Display. Hit "Find plates", then select the POSS-I O or POSS-E Red Plate and hit "Extract Image from Selected Plate".
None of of the other plates, nor SDSS reveal the circular feature. Hence the conclusion of it being an artefact.
The image Akarsh linked to is probably the best the creator could come up with given the quality and framing of other plates. It's a pity artefacts such as this one are not catalogued, separately, as there are plenty to "discover" (pun intended).