De Vaucouleurs Atlas Type: SB(r)b
Telescope: CTIO 1.5-m
North left , East down
Field Dimensions: 5.8 x 4.5 arcminutes
RC3 Type: (R')SB(rs)ab
RSA Type: -----
Surface Brightness Range Displayed: 19.0-26.0 mag per square arcsec
Absolute Blue Magnitude: -21.6
De Vaucouleurs Atlas Description:
This large southern spiral is a very good example of its type. Although the ring looks broken on one side of its minor axis, it is actually a complete feature that is weak in the northwest quadrant. The face-on orientation shows that the ring is elongated along the bar axis, as in NGC 1433 . The spiral structure breaking from the ring region is complex, and initially is tightly wrapped around the ring. These arms can be followed into the outer disk where a well-defined two-armed pattern dominates. Beyond this two-armed pattern, numerous spiral segments, extending to much larger radii, dominate the morphology. Buta (1995) showed that in an I-band image, these distant segments are much less prominent, and the inner two-armed pattern takes the approximate form of an R1' outer pseudoring . This suggests that the outer spiral segments lie well beyond the OLR in NGC 3313 .
The structure inside the inner ring includes two weak leading dust lanes in the bar, and in the center there is a very regular, circular nuclear ring which is partly overlapped by a bright foreground star. In the color index map, this ring shows enhanced blue colors.
Although the spiral pattern in NGC 3313 looks rather open, we adopt Sb for the type based on the main two-armed inner spiral pattern and the general degree of patchiness of the disk.