The Caldwell Objects

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within as little as 24 hours. The researchers also
noticed that the variable star brightened by 1.3
magnitudes during their observing period. From
these findings they deduced that the nebula's
apparent changes were caused by the shadowing
effects of moving clouds well within 1 a.u. of the
variable star. Similar shadow play occurs in
Hubble's Variable Nebula (Caldwell 46).
Our Caldwell target couldn't be easier to
find. It is 40' east-northeast of 5th-magnitude
Epsilon (ε) Coronae Australis in the northern arc
of the Southern Crown. I use 7x35 binoculars to
confirm that I've located Epsilon Coronae
Australis, which is 6° south of the midpoint in the
base of the Sagittarius Teapot. Then I hop about
½° east to the 7th-magnitude double star
associated with IC 4812. (Here's a challenge: can
you see this star with the naked eye?) The NGC
6726-7 complex should appear as a fuzzy "star"
about 15' to the northeast of that double star. Our
target, NGC 6729, is a fainter "fuzzy" star
immediately southeast of NGC 6726-7.
Although we are ostensibly pursuing
Caldwell objects here, let's take the time to
acquaint ourselves with some of the region's
other wonders before rushing on to NGC 6729.
Through the 4-inch at 72x the double star
associated with IC 4812 is a beautiful pair of soft
blue orbs of near-equal brightness; they are
separated by 13". The easternmost star is the
brighter of the two at magnitude 6.4 and has a
slightly evolved spectral class of B9.5IV; its
magnitude-6.7 companion has a main-sequence
spectral class of 57/8V. NGC 6726-7 is a 9' x 7'
haze surrounding two other stars oriented northnortheast
and south-southwest. The brighter
member of that pair seems to shine with a
slightly warmer (yellower) hue than the blue
stars in the 7th-magnitude double. The
magnitude-7.2 star responsible for
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illuminating NGC 6726, the nebula's southwestern
portion, is of spectral class B 9 The N .
brightness of NGC 6727, the nebula's northeastern
portion, is regulated by TY Coronae
Australis, a variable star that fluctuates irregularly
between magnitudes 8.7 and 12.4. NGC
6726-7 has a high surface brightness, and if you
doubt you're seeing it, just compare it to your
view of the 7th-magnitude double star, which
should be fuzz-free in a small instrument. With a
careful gaze at 72x the nebulae appear mottled.
Hints of a ray-type structure can be seen, as well
as a large "brow" of nebulosity, which arcs to the
northwest over both of the involved stars.
At 130x NGC 6726-7 shatters into several
fragments. The two most intense patches form a
ten-pin shape, with the brightest portion
surrounding the brighter star to the southwest.
The "brow" to the northwest comprises two
conjoining arcs of light, each of which bristles
with faint tendrils that extend radially away from
them. Take the time to study the intriguing
nebulosity around TY Coronae Australis. In it I
see two dense knots, one to the east and one to
the north of TY. With a prolonged look and
averted vision, dim patches, knots, and
Deep-Sky Companions: The Caldwell Objects