The Caldwell Objects

NGC 5822. Don't be surprised if you think you
see hints of resolution. This is somewhat illusory,
though. While several 10th-magnitude field stars
dapple NGC 5823's face, they are foreground
stars; NGC 5823's true members shine at
magnitude 13 and fainter. The cluster may also
look segmented, but this is another illusion
created by a pair of roughly 8.5-magnitude stars
15' to the southeast. The pair looks fuzzy in small
binoculars.
At 23x in the 4-inch the region is most
complex. NGC 5822 dominates the field. It is so
open and patchy and the surrounding swath of
Milky Way so rich that it is difficult to fathom its
true extent. Furthermore, and most confusingly, a
most peculiar gathering of some 20 suns
(magnitude 8 to 11) lies 50' southwest of the core
of NGC 5822, where it trends east-west and
covers an elliptical area 20' long. This elliptical
cloud's brightest stars favor its west side;
included among them is the Mira-type variable Υ
Lupi, which dips from magnitude 8.2 to 15.2,
then brightens, every 401 days. To my
knowledge, this "cluster" (RA 15 h 01 m ; Dec.
88
-55° 00') does not appear on any star atlases as
such, so it may be just a dense patch of Milky
Way. However, this region of the Milky Way has
been poorly studied by professionals; someone
should obtain photometry on these stars to see if
they are related. A faint tail of dim suns runs
northward from our new "cluster" toward NGC
5822, while another travels an equal distance (50')
to the southeast, where NGC 5823 lies. Together
these three clusters form a large equilateral
triangle and look as if they are but pieces of one
massive "supercluster" spanning nearly 1½° of
sky.
Actually, that idea is not totally out of kilter.
In fact, the visual confusion provided by these
clusters and the Milky Way has had professional
astronomers scratching their heads, too. In 1968
Mary T Bruck . (University of Edinburgh,
Scotland) suggested that NGC 5823 might be
physically related to NGC 5822. And while
Dennis W Dawson . (Western Connecticut State
University) all but disproved that notion 10 years
later, he introduced another concept — namely,
that NGC 5823 might not be a cluster at all! His
study of its red-giant stars showed a wide
scattering of physical properties, implying that
the stars are not related and, therefore, that NGC
5823 is not a cluster. Furthermore, the density of
stars in NGC 5823 seemed to be no different than
that of the surrounding Milky W Such a is y the .
difficulty with open clusters in extremely rich
regions of the galactic plane. That being said, the
most recent studies of NGC 5822 and NGC 5823
have all but proved they are independent clusters
with dissimilar distances and ages. Writing in the
August 1981 Astronomical Journal, Kenneth A.
Janes (Boston University) asserted that Dawson's
study was flawed because it included stars across
too large an area. Janes's own study stayed
within 10' of the cluster's core, and it showed
stronger relationships between the cluster's
putative
The Caldwell Objects 349