The Caldwell Objects

would John Herschel suddenly fault Dunlop for
doing the same? I cannot find anything wrong
with Dunlop's description of the object now
known as NGC 300. Johann Louis Emil Dreyer
described the galaxy in his New General Catalogue
as a "complex object with several nuclei." And
photographs clearly show the "nebula" studded
with field stars and Η II regions. Herschel's
motion to discredit Dunlop seems even more
surprising in light of his own discussion of the
object, which placed it among "nebulae of
irregular forms having a tendency to several
centres of condensation," such as NGC 55 in
Sculptor (Caldwell 72) and NGC 1950 in
Horologium. That Herschel disagreed with one
aspect of Dunlop's visual description of NGC 300
hardly warranted robbing Dunlop of his
discovery.
In photographs NGC 300 displays a barless
spiral with wide, loosely wound arms and a tiny
nucleus; it looks like a miniature, mirrorreversed
version of M33, the Pinwheel Galaxy in
Triangulum. Like M33, NGC 300 has two dominant
S-shaped spiral arms laced with dark lanes
and starry clumps; two other feathery arms,
forming a weaker S, complete the pinwheel
pattern. We see the galaxy's disk 46° from face
on. Its true diameter is 22,000 light-years (56
percent smaller than M33's), and it has a total
mass of about 30 billion Suns. The galaxy is receding
from us at 145 km per second.
NGC 300's disk has an underlying population
of old stars with ages between 0.1 and 10 billion
years. Deep infrared images have revealed that
the brightest stars in the galaxy's central region
are massive red supergiants. CCD spectra have
confirmed the presence of 28 supernova
remnants. Together with a similar number in
NGC 7793, these represent the first large sample
of supernova remnants identified in a galaxy
beyond the Local Group. Thirty-four planetary
nebulae, 88 Η II regions, and 7 ring-
70 & 72
like nebulae also have been identified in the
galaxy's disk. The ringlike objects appear to be
bubbles blown by winds from unusually hot
stars; they span anywhere from 160 to 910 lightyears
in diameter.
Furthermore, a search for Wolf-Rayet stars
with the New Technology Telescope has confirmed
the presence of nine such stars within
NGC 300. Although NGC 300 is often referred to
as the Twin of M33, NGC 300 has twice as much
of its mass in the form of cold hydrogen as does
M33 and only half the northern Pinwheel's
intrinsic luminosity. No nebular emission has
been found within the galaxy's bright nucleus,
which, most likely, is an unresolved compact
stellar cluster similar to the nucleus of M33. X-ray
observations of NGC 300 by the Rosat satellite
found evidence for a black-hole-bearing binary
star, several supernova remnants, and Η II
regions — but found the galaxy otherwise
"unremarkable."
From a dark southern observing site, NGC
300 is visible in 7x35 binoculars as a roundish
glow just about 12' southwest of an 8.5-magnitude
star, which could be a variable, and about
2.5' northeast of a lOth-magnitude star. Sky Catalogue
2000.0 and the Observing Handbook and
Catalogue of Deep-Sky Objects list the galaxy's blue
(B-band) magnitude as 8.7. Walter Scott Houston
found its light to be equal to that of a magnitude-
8.5 star, but he also reminded us that since the
galaxy's "light is spread over so large an area the
surface brightness is low" Thus it would not
surprise me if NGC 300 appears fainter from
north temperate latitudes, where it can never get
far above the horizon. The Deep Sky Field Guide
lists its visual magnitude as 8.1. Using 7x35
binoculars I got a visual magnitude of 7.2. Try
making your own estimate.
In the 4-inch NGC 300 looks very complicated
at 23x. Several bright stars are superimposed
on the galaxy, which should frustrate
The Caldwell Objects 279