The Caldwell Objects

position updates to (2000.0) R.A. 11 h 35.7 m
and [Dec] -63° 01’; the range updates to
approximately (2000.0) from IP 35 m to IP 36 m,
and from -62° 47' to -63° 13'. The [Digitized]
Sky Survey shows at this position a very
bright star (Lambda Centauri), and faint
nebulosity around it that is mostly
overpowered by the star. There is also a very
rich background of stars here, which may be
a cluster.
IC 2948. The IC lists this as Frost 790 with the
following description: "Most extremely
large." In the Harvard Annals, Frost 790 is
described as a "Neb. patch ext. from 11 h 30.6 m
to IP 38.l m, and from -62° 28' to -63° 14'." The
position updates to (2000.0) [R.A.] IP 38.8 m,
[Dec] -63° 31' and the range updates to
approximately (2000.0) from 11 h 35 m to 11 h
43 m and from -63° 01' to -63° 47'. At the
precisely given position, the DSS shows
nothing unusual. However, with histogram
equalization [an image-processing technique],
there are concentrations of nebulosity to the
northwest, north-northeast, and northeast. Α
1° DSS image shows nearly the full 1° square
filled with nebulosity, with the patches
mentioned above being the brightest
portions. Clearly, [Yerkes Observatory
astronomer Edwin Brant] Frost [(1866-1935)]
had the whole area in mind and not just the
brighter concentrations. It is also clear that
this is the (larger) nebulosity to the southeast
of IC 2944 and is not IC 2944 itself.
Cr 249. Collinder 249 is listed by Collinder as
IC 2944 (more comments on this follow). He
describes it as 40' x 15' in size, 2.7 total
magnitude, and 25 stars total. He adds that
Lundmark lists it as 65' x 40' in size, 2.9 total
nebulosity. Areal density of fainter stars the
same as in surroundings (from star-counts)."
Collinder goes on to present a photo-
graph of this cluster, copied from the Franklin-
Adams charts, showing several bright stars in
nebulosity. I couldn't easily match this photo
to a DSS image of the area, so I checked the
Franklin-Adams chart (no. 18). I was surprised
to find that Cr 249 in fact is a very large object,
consisting of all of the stars around IC 2944
and IC 2948, and then some! Generally it is the
whole group of stars extending from Lambda
Centauri (and IC 2944) on the northwest, down
to a pair of stars at 11 h 41.8 m and -63° 49', thus
filling [an] oval about 1 degree in length!
Lundmark's size estimate of 65' x 40' thus
matches well.
Thus, Collinder 249 is not IC 2944. Frost
mentioned nothing about a star cluster in his
descriptions of either IC 2944 or IC 2948. And
more importantly, the group of stars is
centered on IC 2948 and not IC 2944 as
Collinder's identification and (incorrect)
position implies. These two errors by Collinder
are obviously the source of all the later
confusion about the objects here.
In summary, the nebula IC 2944 is pretty
much concentric on Lambda Centauri. IC 2948 is
the nebulosity to the southeast, and it is distinct
from IC 2944. And the entire area's ensemble of
stars is the cluster Collinder 249. There
apparently is no cluster centered on Lambda
Centauri, though it does have a rich background
of Milky Way stars. (Incidentally, Lambda
Centauri itself is much closer than the cluster; the
Hipparcos satellite has pegged its distance at 410
light-years.)
magnitude, and 40 stars total. It is called a Another Caldwell mystery solved! Despite
"Neb. cl." so the involved nebulosity was its tortured history, and the way it has been mis-
clearly recognized. Collinder calls it " replica A represented on star charts, we can now engage
in Southern Sky of Pleiades" and writes, "This
is a chain of bright stars with
100
ourselves in finding the true Lambda Centauri
Cluster with confidence. (Any nebulosity seen
The Caldwell Objects 399