>On Saturday night at CalStar I was shown a globular cluster in NGC
>6946 in a 15" Dob.
>
>I had never heard of this object before, and found it astonishing
>that any globular could be seen
>at such a distance. Globulars I've seen in M31 are less remarkable
>than the brigth glow the one I
>was being shown was.
>
>I suspect it is really an HII region, and not a globular cluster.
>Doing google searches on NGC
>6949 shows that it is unusually rich in HII.
>
>Can anyone confirm that there is a bright HII region visible in this
>galaxy? Or, can anyone point
>to some literature describing a bright globular in it, visible from
>over 15M light years?
>
>Thanks,
>
>Mark
Hi Mark,
We first started talking about 6946 at dinner Saturday night when
Jim mentioned that the new issue of Scientific American has a good
article on globular cluster formation, including the fact that some
globular clusters are much newer than the ancient clusters of the
Milky Way. I haven't seen the article, but had learned the same
thing over the last year or so of the galactic and extragalactic
globular cluster observing project I have been doing. I had
observed the 6946 cluster as part of my extragalactic observing
project last year at CalStar, and remembered the object as an
observable example of a young cluster. Fortunately it is well
illustrated in the image of 6946 found in that Concise Catalog of
Deep Sky Objects from Springer that we were looking at with you over
dinner. Jim and I both tracked it down again this year using the
diagram in that book, which specifically highlights the region as a
young globular cluster.
For a primary literature reference, see:
Larsen, S. S. , Brodie, J. P., Elmegreen, B. G., Efremov,
Yu. N., Hodge, P. W. and Richtler, T. 2001: ``Structure and
mass of a young globular cluster in NGC 6946'',
ApJ 556 , 801-812 (astro-ph/0104133)
The entire paper is available online at: http://adsabs.harvard.edu/bib_abs.html
The brief synopsis is that this region appears to be an example of
supermassive star cluster that has formed in the last 15 million
years, and whose structure, properties and mass suggest that it will
remain gravitationally bound as a globular cluster. A young
globular to be sure, but that is part of why it is an interesting
object.
David Kingsley