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SB (r) : This is the typical ``Phi-shaped'' barred spiral. It has a fairly large, elongated nucleus with weak spiral dark lane in a strong, narrow bar along the major axis of an elliptical ring marking the edge of the lens. Two main arms start tangentially from the ring near the extremities of the bar (i.e. at right angles to the bar); one or two fainter arms branch out from breaks in the ring near its minor axis. In early stages the main arms tend to form an outer, circular (R) structure, as in NGC 1433 (25); in later types the breaks in the ring tend to produce slightly hexagonal shapes. Examples are NGC 1433 (illustrated from S 74"), Sa or Sab, NGC 3185, NGC 3351, Sab (26), NGC 2523, Sbc (27).

NGC 4262 13. NGC 4262 (P 200"): SB (r) 0 o. Small nucleus in short, stubby bar (stringer near extremities) in bright diffuse lens. The nucleus appears large on this image taken in yellow light. Compare with 9, 15 and 16. NGC 1512 14. NGC 1512 (S 30"): SB (r) 0 +. Small, elongated nucleus on narrow, bright bar marking the major axis of elliptical ring; the ring is stronger near the extremities of the major axis. Traces of spiral arms or arcs in weak envelope outside ring. Compare with 8 and 25; NGC 1510 (E0) is at left near edge of field.
NGC 2859 16. NGC 2859 (P 200"; inset P 48"): (R) SB (r) 0 o. Fairly large nucleus on weak bar marking major axis of little elongated lens, slightly stronger near rim where bar appears brighter. Faint outer ring structure from which emerge two very weak spiral arms or arcs. No spiral structure in lens. Compare with 12, 14 and 15. NGC 1433 25. NGC 1433 (S 74"): (R') SB (r) a. A small, elongated nucleus whose major axis is tilted at 45° to a long, narrow bar along which run filaments of dark matter. The bar marks the major axis of an elliptical ring from which emerge two faint arms near the extremities of the bar and two weaker branches forming an incomplete outer ring (inset). Compare with 14, 26 and 29.
NGC 3351 26. NGC 3351 = M95 (P 200"): (R') SB (r) ab. The nucleus and bar are enhanced on this photograph taken in yellow light; the elliptical ring appears circular or slightly hexagonal by projection foreshortening; note the two main arms emerging from ring near the extremities of the bar and weaker branches. Compare with 25, 27 and 30. NGC 2523 27. NGC 2523 (P 200"): SB (r) bc. The nucleus and bar are still strong, but the ring is narrower and knotty; two main spiral arms, narrow and knotty (one with branching) emerge from the ring near the extremities of the bar; additional, weaker arms start near minor axis of elliptical ring (here appearing circular in the projection). Note slight asymmetry. Compare with 26, 28 and 31.
NGC 3367 28. NGC 3367 (P 200"): SB (r) cd. The nucleus and bar are smaller and fainter; the elliptical ring is weaker and begins to break up into knots; the arms are branching and filamentary; note strong asymmetry. Compare with 24, 27 and 31.  

SAB (r) : has a fairly small, little elongated nucleus in a fairly broad and faint bar marking the major axis of a little elongated ring from which several spiral arms branch out. The main arms have a slight tendency to ``return'' inwards. Examples are NGC 1832, NGC 7531, Sab, NGC 6744, Sbc (illustrated from S 30"). Some, like NGC 6902, NGC 6935, Sa, NGC 6937, have only very faint traces of a bar and mark the transition towards SA (r).

NGC 3032 15. NGC 3032 (P 200"): SAB (r) 0 o. Fairly large, elongated nucleus on short, bright stubby bar, surrounded by dark ring or arcs in bright lens. The envelope does not show up on this print. Compare with 3, 7 and 13.

SAB (rs) : this is the most general mixed type involving all possible transitions between the main typical patterns. An almost infinite variety is possible here, but for classification purposes the main characteristics of this hybrid type are: a small bright nucleus in a broad, diffuse bar with some spiral structure in the lens. The bar crosses a nearly circular or often hexagonal pseudo-ring formed by the inner sections of the spiral arms. A very good example is NGC 4303 (M61), Sbc (illustrated from IR 20"); other examples are NGC 3145, NGC 6814. At a later stage this mixed structure is well illustrated by the central regions of NGC 5457 (M101) and NGC 6946, both Scd.

NGC 6873 11. NGC 6873 (S 74"): SAB (rs) 0 o. Fairly small nucleus in elongated lens with dark ring or crescent, surrounded by extensive, bright envelope. Compare with 3, 7 and 9.

Examples of irregular later stages of the spiral sequences are:

NGC 6873 37. NGC 1613 (P 48"): I Bm. The residual structure includes the well resolved axial bar and asymmetrical bright patch rich in supergiants and emission objects. Note characteristic asymmetry. Compare with 36 and 38. Dwarf I 38. Dwarf I in Andromeda (2h31, + 40°19') (P 200"): dIB (s) m. The characteristic structure of the late-type SB (s) spirals is still recognizable, including axial bar (foreshortened in the projection), with embryonic spiral arms emerging at its extremities; one of the arms can be faintly traced to the left and lower part of the field. Compare with 36 and 37.

Examples of peculiar lenticulars and non-magellanic irregulars are:

NGC 1947 56. NGC 1947 (S 74"): SA0p. Little elongated, smooth nebulosity, rather similar to elliptical galaxy or to spheroidal bulge of early spiral, cut by two slightly curved lanes of dark matter on one side of nucleus. There is no trace of spindle or outer spiral structure. NGC 3077 57. NGC 3077 (P 200"): I (0) or SAB0p. Little elongated, smooth nebulosity marked by irregular patches of dark matter; two of them emerging on both sides near minor axis simulate embryonic spiral pattern as seen in nuclear regions of SAB (s) 0/a. Has contrasting early spectral type and advanced color index. Compare with 15.
NGC 4753 58. NGC 4753 (W 100"): I (0) or SB ? (s:) 0 +p. The inner isophotes (inset) are elongated at right angles to the direction of the major axis of the outer isophotes. The nuclear region is crossed by complex dark lanes which appear to be on the near side below the small nucleus and on the far side above it (see inset). This could be interpreted as the near end-on (``along'') view of the bar and lens of the armless SB (s) 0/a object. Compare with 55 and 56. NGC 4691 59. NGC 4691 (P 200"): (R) SB (s:) 0/ap. The weak outer whorls in the envelope (inset) show that this system is seen nearly face-on; note the complex structure of the bar crossed and surrounded by patches and curved lanes of dark matter. Compare with 52, 57, 58 and 60/61.
NGC 3034 NGC 3034
60/61. NGC 3034 = M82 (P 200"): I (0) or SB (s:) 0p. This is interpreted tentatively as the ``broad-side'', nearly edge-on view of the bar and lens of an armless SB (s) 0/a object. Has contrasting early-type spectrum and advanced color index. Compare with 53, 57 and 59. Note especially the great similarity between 59 and 61 and the characteristic ``crossing-over'' of the main dark lane in the nucleus 1.


1 This interpretation of the non-magellanic irregulars is consistent with their luminosities, colors and dimensions). It also makes it possible to understand the rapid, solid-body rotation observed along the major axis of M82 (N. U. Mayall, in ``Problems of Cosmic Aerodynamics'', U.S. Central Air Documents Office, p. 181, 1951).

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