Quote:
Originally Posted by Steffen
From looking at the catalogs rather than the sky (not equipped to view mag 15 objects, I’m afraid) it appears that there are two objects at that location – planetary nebula PK 288+08.1 and spiral galaxy PGC 34540, both around mag 15. Not sure whether they are actually two different objects or one that has been classified variously.
|
Hi Steffen,
Thanks for looking but Dennis and I took the thread on a serendipitous
segue to a different object some 194 arcseconds away that had caught
Dennis's eye.
The story so far :-
ESO 2-216 (11:18 09.77 -52 10 02.7 ICRS)
However, just to go back to the original object in the title of thread,
ESO 2-216 had originally been classified as a galaxy in the ESO galaxy
survey. This then got swept up by the PGC catalog and given a PGC
reference number of PGC 34540. However, this is incorrect and there is
no galaxy there.
ESO 2-216 also appears in PK with an identifier PK 288+08.1
That is correct and indeed ESO 2-216 is a planetary nebula.
In the images, one can discern ESO 2-216's shell as a ring, and the bright
blue bar on its north side appears reminiscent of those on M27.
This arc was probably what confused the ESO survey in thinking it was
a galaxy.
My reaching out originally was in the hope that someone might fancy
imaging Planetary Nebula ESO 2-216 to get a better view of its ring
and that bar. Dennis happened to be testing some gear and grabbed
some shots.
So there is only one object there, not two.
One has to always be careful with the PGC and PK catalogs.
I tend to think of them as the Magritte of catalogs - "This is not a catalog".
Actually, that is not entirely fair. However, both catalogs are
primarily compilations of other
primary source survey catalogs.
So if you or I are doing a survey of galaxies and we publish the
"Steffen-Gary Catalogue of Impossibly Dim Galaxies", whenever they
compile PGC they are likely to include not only all the great new stuff
we found but all our screw-ups too.
Likewise, PK is a compilation
of other planetary nebula surveys.
Dennis's Serendipitous Object (11:18:27.83873 -52:08:21.3072 ICRS)
Whilst imaging ESO 2-216, Dennis's eye was caught by an object some
194 arcseconds away which he thought appeared "fuzzy" in a way not matching
his usual profile of what looks like a star.
This thread has been mulling over that object since.
We know it has a Gaia star survey designation and we know from
database searches there are no DSO objects at or near this
location. It appears to have a little 'bump' in it which is not a diffraction
spike. Might be two stars overlapping or perhaps a DSO such as another
PN with a shell. Gaia lists it as 20th magnitude in whatever color filter
it uses.