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The Caldwell Objects

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5 2<br />

NGC 4697<br />

Type: Elliptical Galaxy (E6)<br />

/ Lenticular Galaxy (SO)<br />

Con: Virgo<br />

RA:12 h 48.6 m<br />

Dec:-05° 48'<br />

Mag: 9.2; 9.0 (O'Meara)<br />

Dim: 7.1' x 5.4'<br />

SB: 11.6<br />

Dist: 76 million light-years<br />

Disc: William Herschel, 1784<br />

W. H ERSCHEL: [Observed 24<br />

April 1784] Very bright, very<br />

large, suddenly much brighter<br />

in the middle. Resolvable<br />

nucleus. (Η I-39)<br />

GC/NGC: Very bright, large,<br />

little extended toward position<br />

angle ~45°, suddenly much<br />

brighter in the middle to a<br />

nucleus.<br />

NGC 4697 is AN ENORMOUS ELLIPTICAL<br />

system in the southern extension of the Virgo<br />

Cluster and somewhat of a problem child. <strong>The</strong><br />

problem is its morphology. In 1925 Edwin<br />

Hubble introduced a system for categorizing<br />

galaxy types, in which he recognized three main<br />

varieties: ellipticals, "normal" spirals, and barred<br />

spirals (see the discussion on page 139).<br />

Ellipticals, Hubble said, were amorphous objects<br />

"ranging from globular to discus shaped," and he<br />

organized them according to their flatness. <strong>The</strong><br />

most spherical galaxies he called E0, and the<br />

most flattened ones he called E7. Hubble's<br />

scheme has been slightly revised today, but the<br />

framework is essentially<br />

52<br />

the same. Until recently astronomers recognized<br />

NGC 4697 as a typical elliptical system, though<br />

they disagreed on its exact shape; various sources<br />

still list the galaxy as either an E4, an E5, or an E6<br />

system. Recent observations have upped the ante,<br />

suggesting that NGC 4697 is an early-type disk<br />

galaxy with a lenticular (lens-shaped) body — an<br />

S0, in short (see <strong>Caldwell</strong> 53 for another<br />

example).<br />

Both ellipticals and lenticulars can be lensshaped,<br />

and both have very little gas and dust (in<br />

fact, some ellipticals may have none). Unlike<br />

lenticulars, however, ellipticals show no central<br />

bulges, nor structures like disks or spiral arms. A<br />

classical elliptical galaxy is simply<br />

<strong>The</strong> <strong>Caldwell</strong> <strong>Objects</strong> 207

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