The Caldwell Objects

nebulosity when he viewed the region with a 9inch
telescope. With his 18¼-inch reflector John
Herschel noted a "faint nebula, in which the
preceding [western] part of the cluster is involved."
Ernst Hartung has definitely seen a
nebulous glow in his 12-inch reflector; he
recorded "faintly luminous nebular material...
about 100" across which extends irregularly
towards the cluster." He also noted that "[a] clear
dark night and good aperture are needed for this
object." I know of no other visual reports of NGC
6193's bright nebulosity. How small a telescope
will show it? And how will it look if a nebula
filter is employed?
Under medium or high magnification HD
150136 can be resolved into a fine double star
with a magnitude-6.8 companion that was
82
9.6" to the west of the magnitude-5.7 primary star
in 1991. James Dunlop discovered that
companion in 1836, and the pair has shown little
change in separation or position angle since that
time. Also in 1836, John Herschel discovered a
10.5-magnitude companion (13.4" at 160° in 1938)
as well as a magnitude-11.4 companion at 14" and
15° (which also date from 1938; neither pair has
changed much since its discovery). The real
challenge, however, is spying HD 150136's
magnitude-8.5 companion, which in 1938 was a
mere 1.6" off at a position angle of 15°; I did not
see this when I looked. Finally, HD 150136 itself
is a spectroscopic binary star, one of many in the
cluster. The cluster is receding from us at an
overall speed of 32 km per second.
The Caldwell Objects 331