[AZ-Observing] NGC 6882 and NGC 6885

Just a few comments here on the identification of NGC 6882 and NGC 6885. I 
cover this topic in detail (more than a full page of text plus a DSS 
image) in my book "Star Clusters" with Steve Hynes (Willmann-Bell, Inc., 
Richmond, 2003), pp. 187-189.  So I'm not going to repeat all that here, 
but will just respond to some points in the messages (in the az-observing 
digest) from Monday.
- It's not entirely certain, but it does look like NGC 6885 (definitely 
identified) = NGC 6882 (see book for full details).  Examining W. 
Herschel's original observations of these (available at the RAS library in 
London and on microfilm) might help to verify this once and for all, but 
to my knowledge that has not yet been done.  Harold Corwin's notes, which 
Bob Erdmann quotes, are a little out of date.  I had indeed at one point 
thought that NGC 6882 might be a circlet of stars 15' north of NGC 6885 
(at WH's given position for NGC 6882) but I was convinced by Harold that 
that was unlikely (and I told him so).

- The actual group of stars was noticed by Trumpler to possibly consist of 
two parts, a coarse 22' diameter group of bright stars including 20 Vul, 
and a smaller and slightly fainter 8' grouping included on the NW side of 
the larger group.  In my experience, this is detectable visually, but is 
not obvious.  In any case, as you can imagine - and as detailed in our 
book - the existence of two possible groups here and two NGC numbers (and 
then Trumpler and Collinder numbers) has lead to lots of confusion about 
identities here.

- I think Steve O'Meara has a good discussion of this issue also, in his 
"Caldwell Objects" book, but I don't have my copy handy to check.  He and 
I observed this object at length at one point with the Warren Rupp 
Observatory (Ohio) 31-inch f/7 reflector and could easily see the two 
Trumpler "groups".

- Brian Skiff may be correct that there is no cluster here at all, but the 
large group at least is certainly obvious visually.  I have not done any 
checking to see if modern studies have been done about the existence of a 
cluster, but Trumpler at least - based on the admittedly poor data he had 
available - believed there were two real clusters here.

- Thad Robosson noted that both the Millennium Star Atlas and the AL 
Herschel 400 include the two clusters here under the two NGC designations. 
 This is probably simply because they had been relying on modern (late 
20th century) catalogs of star clusters which had the designations 
confused, due to the earlier mistakes by WH, Trumpler, and Collinder.

I hope that covers the major points in question.  In any case, I hope 
folks will go out and take a look at this "cluster" or whatever it is and 
see it for themselves.

- Brent


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