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Old 26-09-2013, 09:28 AM
Weltevreden SA's Avatar
Weltevreden SA (Dana)
Dana in SA

Weltevreden SA is offline
 
Join Date: Apr 2012
Location: Nieu Bethesda, Karoo, South Africa
Posts: 216
Thanks for posting your image, Jon. It helps clear up the actual globular versus the confusing field stars. I checked several other images to confirm (Google NGC 6717 for the list), and all point to the same thing: the globular is the fuzzy spot in the middle of the concentration in your image, while the surrounding brighter stars above, below, & to the left, are field stars. This stands to reason, because if cluster members they would be on the outskirts of the globular. Globular outskirts are populated by the cluster's faintest stars—many to sooner or later escape if they near the L1 or L2 Lagrange points moving at above the escape velocity of the cluster. The field stars in your image are too bright to be outliers. I don't know of any GC whose outer members outshine its core population. These field stars have apparently tripped up a number of observers. This Aug 2006 thread on Cloudy Nights reports several resolutions, but the cluster's brightest red giants are only mag 14 and brightest horizontal branch stars are 15.6, which are below the limits given the apertures quoted. Also, Sagg is pretty far south for N American observers. (One more feather in the cap of we 'Southies'.)

Thanks again for observing & imaging. 6717 is a very tricky cluster, and therefore lots of fun. If not for you, I would have gone through life in clueless bliss. =Dana in SA
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