The Caldwell Objects

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that core is an obvious "spiral arm": a bright to one another. After analyzing two possible
string of stars juts first to the west, then to the cluster concentrations on National Geographic
north; a weaker extension of dim suns continues Society-Palomar Observatory Sky Survey prints,
to the east and back to the triangle. Paralleling Braun's team determined that the number of stars
that eastward-trending arm to the north is an in the putative cluster does not exceed the
isolated fishhook of equally dim suns. Opposite expected background count. Furthermore, the
the fishhook, in turn, is an isolated triangle of researchers plotted color-magnitude diagrams for
faint suns in the cluster's northernmost reaches. the two possible cluster regions; again, no
The dark lane separating the two halves of the evidence for a star cluster was found. Proper
cluster abuts a north-south-trending string of motions were calculated using catalogs dating
stars that curves to the east. The cluster's from 1902 to 1996 along with the Hipparcos
northeastern half also has a triangular array of satellite database. This yielded only a hint of a
stars, with angular strings of stars emanating small open cluster. Finally, the scientists
from it. Higher powers do not add to the view of examined the proper motions of stars within radii
the cluster, but do use them on the double star. of 10' and 20' around the two putative cluster
Once you've gone through this visual centers. No significant cluster signature emerged.
exercise, consider this: in a 1999 paper W G. . The scientists conclude that if NGC 7243 is really
Braun (Bonn University, Germany) and two a star cluster, it consists of only a few members.
colleagues investigated whether NGC 7243 is a But no final determination has been made. The
single open cluster, a double cluster, or a group cluster is 76 million years young — similar in age
of bright stars without any physical connection to the Pleiades.
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Deep-Sky Companions: The Caldwell Objects