The Caldwell Objects

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an oval "shell" filled with ancient starlight and
surrounded by a halo of senior globular clusters.
In ellipticals, stars concentrate toward the center
and form a nucleus of old, low-mass suns.
William Herschel aptly described this nuclear
concentration of light as "suddenly much
brighter in the middle." Herschel also believed he
could resolve the nucleus of NGC 4697, but his
eyes fooled him; the galaxy is 76 million lightyears
away, more than 30 times the distance of
the Andromeda Galaxy. Resolving its individual
stars would have required supernatural vision.
(In Herschel's defense, let me note that many
ellipticals do appear mottled through the
eyepiece. I have yet to encounter an explanation
for this illusion, though I believe a sprinkling of
field stars can contribute to it.) There is one other
key difference between ellipticals and spirals.
Ellipticals lack the merry-go-round simplicity of
spiral disk structure and dynamics. Stellar orbits
in an elliptical galaxy are haphazard; imagine an
airport where planes are landing and taking off
in all directions without the guidance of an airtraffic
controller.
In photographs NGC 4697 looks very much
like the textbook definition of an elliptical —
completely smooth, its brightness fading evenly
from center to edge. Or does it? New technology
has opened new windows on the universe, giving
us fresh looks at old wonders. The Infrared
Astronomical Satellite, for instance, discovered a
stellar disk (one contributing 2.1 percent of the
galaxy's total luminosity) lying along NGC 4697's
major axis. If we stick to the strict definitions of
elliptical and lenticular galaxies, this seems to tilt
NGC 4697 toward the lenticular category. Further
evidence for NGC 4697's lenticular nature
appeared in a 1996 Astronomy and Astrophysics
paper by Herwig Dejonghe (Ghent University,
Belgium) and three colleagues. Using the New
Technology Telescope in Chile, they found a
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nuclear dust lane 3.4" (1,300 light-years) from
NGC 4697's center. Along with earlier evidence
for a strong disk component to the galaxy, this
bolstered the notion that NGC 4697's spheroid
may simply be a lenticular galaxy's nuclear bulge.
As astronomers scrutinize more elliptical
galaxies, they may discover that stellar disks and
dust lanes are commonplace in all late-stage
ellipticals. If so, we'll need another way to
discriminate between highly flattened ellipticals
and true lenticular systems.
NGC 4697 is the first object in the Caldwell
Catalog to lie south of the celestial equator. It is
also, surprisingly, the catalog's only galaxy in the
constellation of Virgo. But it is a beauty. In his
Astronomical Objects for Southern Telescopes, Ernst
Hartung describes NGC 4697 as being "an easy
object even for 7.5 cm [3-inch]. The small
elliptical ['s] very bright centre is surrounded by
a hazy envelope." The galaxy is indeed very
bright, and its concentrated glow is visible in
7x35 binoculars. My binocular magnitude
estimate (9.0) agrees reasonably well with the
value listed in the table on page 207.
To find the galaxy start from Porrima, or
Gamma (γ) Virginis, one of the finest double
stars in the sky for small apertures. lust ½° eastsoutheast
of Porrima, a 6th-magnitude star marks
the northern end of a 5°-long string of five
binocular stars. This string, which is oriented
nearly north-south, ends with a magni-tude-6.3
star. Our target is only about ½° northeast of that
star. You can also start at the top of the "sail" of
Corvus, marked by the roughly 3rd-magnitude
stars Delta (δ) and Gamma (γ) Corvi. Now look
for a 5th-magni-tude star forming the apex of a
northward-pointing, near-equilateral triangle.
This star marks the southwestern end of an
obvious 10°-long chain of six roughly 5th- to 6thmag-nitude
binocular stars, which includes 21
and Chi (χ) Virginis. NGC 4697 is only about ½°
Deep-Sky Companions: The Caldwell Objects