SAB (s) : Has a fairly small,
bright, elongated nucleus crossed by a
weak, twisted dark lane in the center of a weak and broad bar marking
the major axis of a faint, diffuse and elongated lens with much spiral
pattern of dark matter having a tendency to run parallel to the
bar. Two main arms emerge near the extremities of the bar along a
smooth, curved path turning sharply just outside the lens; their faint
extremities tend to return to the lens along an almost circular outer
loop, simulating an (R) structure in the early stages. Examples are
NGC 1566 (illustrated from S 30"), NGC 5236 (M83), Sbc,
NGC 4579, Sab and NGC 7392.
55. NGC 3718 (W 60"): SAB (s)
a. The bar is
seen nearly ``end-on'' as in 51. Compare also with 30 and 54. Very
peculiar-looking structures can be produced in the lens and nucleus of
early SB (s) galaxies depending on tilt and orientation of the
bar with respect to the line of sight.
SB (s) : This is the typical
``S-shaped'' barred spiral; it has a small, very bright and
elongated nucleus distorted by a strong, twisted dark lane as it crosses
over from one side to the other of the strong, narrow bar marking the
major axis of a much elongated lens. Two strong, main arms start sharply
at right angles to the bar at both ends and return faintly to it after
completing a turn of a quasi-circular loop. Examples are NGC 1097, NGC 1300,
NGC 1365 (illustrated from S 30"), NGC 5383. Later stages in this
sequence are markedly asymmetrical as NGC 7479, Sc and
NGC 7741, Scd (31). Some, like NGC 1300, have a
third, fainter arm forming a half-ellipse close to the lens and
indicating a transition toward the SB (rs) type.
9. NGC 7079 (S 74"): SB (s) 0
o. Small bright nucleus in short and bright bar
surrounded by very faint traces of spiral arcs in lens; extensive
envelope. Compare with 12 and 13.
10. NGC 1617 (S 30"): SB (s) 0
+. Very small nucleus in short and fainter bar
curving into spiral arms or arcs in lens and envelope. The spiral
pattern is blurred by insufficient resolution here. Compare with 9 and
12. NGC 1291 (S 30"): (R) SB (s) 0
+. Fairly large nucleus on weak bar marking major
axis of little elongated bright lens. Faint outer ring structure from
which emerge two very weak spiral arms or arcs. No ring structure in
lens. Compare with 9, 10 and 16.
29. NGC 7552 (S 74"): (R') SB (s)
small, elliptical nucleus in a bar-like, elongated lens with much
internal structure marked by dark lanes; two main spiral arms (on
stronger) emerge from the extremities of the bar and return each to
the opposite extremity after a halfturn, thus simulating an outer ring
structure. Compare with 10, 23, 30 and Plate X.
30. NGC 1365 (S 30"): (R') SB (s)
upper right inset shows the complex structure of the nucleus due to
the ``crossing-over'' of the main dark lane running along the bar
which is seen here foreshortened in the projection; the two bright and
knotty main spiral arms emerge at right angles to the bar and return
to it after a half-turn (lower inset), thus simulating an outer
ring. Compare with 27, 29, 31 and Plate X.
31. NGC 7741 (P 200"): SB (s)
nucleus becomes inconspicuous in the bar (foreshortened in the
projection); the two main, heavy arms show much branching and
clumpiness; one is much stronger than the other, producing a
characteristic asymmetry. Compare with 27, 30 and 32.
32. NGC 1313 (S 74"): SB (s)
d. Only a very
small nucleus remains in the center of the bar from which emerge two
short arms broken up into clumpy sections. The rest of the spiral
pattern is weak, very irregular and strongly asymmetrical; note also
the asymmetrical halfring on one side of bar. This is the transition
stage towards the magellanic irregulars. Compare with 31, 36 and
36. Small Magellanic Cloud (AE 2"): SB
(s) mp. The spiral pattern is reduced to the axial
bar from which emerge one bright, knotty and asymmetrical arm (above,
right) - including many supergiants - and one faint, smooth arm (lower
left, invisible on print) including no bright supergiant. Traces of
embryonic arms appear at the other extremities of the bar. The
peculiarity is the asymmetrical distortion towards the Large Cloud (top
right). Compare with 32 and 37.
47. NGC 55 (S 30"): SB (s) m
brighter part which is not resolved, except for a few bright emission
knots and complex dark patches, represents a ``rear'' end-on view of
the axial bar; the fainter part (left) which is partly resolved
represents the end-on view of the main asymmetrical spiral
arm. Between them dark clouds obscure the distant parts of the arm;
weak embryonic arms can be identified to the right; compare with 36,
37, 38 and 48.
48. NGC 4631 (P 200"): SB (s) d or
m (sp). The nearly central brighter part which is not
resolved and against which complex dark clouds are projected
represents a ``front'' end-on view of the axial bar; from it emerge
two well-resolved, irregular spiral arms spreading out in opposite
directions. Note characteristic asymmetry. Compare with 32, 38, 42 and
49. NGC 7552 (S 74"): (R') SB (s)
Face-on view; same as 29; note outer loops. Details of bar and lens,
seen from ``above'' are in 52; note pattern of dark matter.
50. NGC 7582 (S 74"): (R') SB (s)
Broadside view; details of bar and lens, seen from ``across'', are in
53; note pattern of dark matter.
52. NGC 7552. Detail of bar and lens.
53. NGC 7582. Detail of bar and lens.
54. Lens of NGC 5383 (W 60"): SB (s)
Seen nearly ``face-on'' as in 49; note structure of nucleus and
pattern of dark matter; compare with 30.
SB (rs) : has a fairly small, very
bright and elongated nucleus crossed by a twisted dark lane, as in
SB (s), in a very strong, very
narrow bar marking the major axis of an elongated lens whose rim is
brighter, especially near the extremities of the bar; this produces a
characteristic ``dash-dot in brackets'' pattern, thus (- o -) from
which emerge two main spiral arms with faint additional branches near
the rim of the lens. Examples are NGC 4548, NGC 4593, NGC 7124 (illustrated
from S 74"). Some, like NGC 4349, Sab, having a brighter lens and
more continuous rim mark the transition toward SB (r).
51. NGC 5566 (P 200"): SB (rs)
view; details of bar and lens, seen from ``along'', are in
inset. There is an (r) structure in the lens which does not
show up on this print. Note lane or layer of dark matter splitting