>Steve wrote: I
>looked up my observing notes for N6946 --
>
>17.5": bright, very large, 6' diameter to main body, elongated 3:2 ~E-W.
>Three arms are visible. A long bright arm is attached at the north side of
>the core and trails to the east. This eastern arm splits; a short fainter
>branch bends south following the core and a long curving bright arm
>terminates with a very faint, very small HII knot. On the west side a
>fainter arm shoots sharply to the north from the core. These outer arms
>significantly increase the diameter of the main body. The galaxy has a very
>large brighter middle but the core is just a very small brighter region close
>SW of the geometric center. A very faint stellar nucleus was seen with
>direct vision. Observation from 12,000' in the White Mountains.
>
>Based on my notes and the image, the "very small HII knot" probably refers to
>the "bubble", although the globular itself is embedded in the feature. Were
>you able to resolve both features?
>
Hi Steve,
I am always amazed by the quality and detail of your observing notes.
I could trace out all the major features of 6946 based on your
description. However, I am not sure we are talking about the same
object when it comes to the HII region and the superstar cluster.
Your "very small HII not" sounds like it was located near the end
of the long curving arm that projects form the North side of the
galaxy core and trails to the east. In contrast, the massive star
cluster/bubble region is found in a much shorter fainter arm that
projects form the south side of the galaxy and projects to the west.
This arm is not one of the main 3 brightest arms of the galaxy, and
is actually located south of the third arm in your description (the
one that shoots sharply to the North from the core).
When I first went hunting this last year at CalStar, I brought with
me an image of the 6946 galaxy. I had circled the corresponding
globular cluster region based on the primary literature reports, and
with the help of the labeled image, was able to pinpoint the exact
location of the bubble/globular complex. I recorded the star cluster
region in 2002 as a
"soft nonstellar glow visible steadily with averted vision and
located the SW side of the galaxy core"
I'm not sure I would have seen it without a labeled chart, and I
could not separately resolve the cluster from the star arcs of the
surrounding bubble region.
When I got a copy of the Concise Catalog of Deep Sky Objects from
Springer this summer, I noticed that the entry for 6946 also
contained an image of the galaxy, with the cluster region
highlighted. I happened to have that book with me when the topic of
young globs came up at dinner, and Jim Everitt and I both used that
diagram to relocate the object two nights ago.
The image in that book also shows a separate bright region located
near the end of the long arm trailing to the east from the galaxy
(on the opposite side from the arm with the bubble/cluster complex).
This region was cut off in Figure 1 of the reference you mention
below, but is clearly visible in wider field images. This was also
visible through the 14.5 inch scope on Saturday night, and could well
be the HII region you refer to.
6946 is a beautiful galaxy, and the fireworks and globular cluster
nursery adds to the interest of studying it through an eyepiece. I
wondered over to the 30 inch telescope at one point Saturday hoping
thinking 6946 would make a great target for the Big Eye. The big
scope was off chasing other interesting targets, however, and I was
soon back at the 14.5 inch scope doing the same.
I would like to add my thanks to everyone who worked hard to make
Calstar such a success this year, particularly Mike Koop and Mark
Wagner. It was one of the highlights of the observing year for me,
a mixture of great people, memorable conversations, and wonderful
observing.
-David Kingsley