The Structure and Dynamics of Ringed Galaxies. II. UBVRI Surface Photometry and H-alpha Kinematics of the Ringed Barred Spiral NGC 1433

The southern galaxy NGC 1433 is one of the nearest examples of a ringed, barTed spiral. It is the prototype of revised Hubble type (R')SB(r)ab, and it includes the three main ring types possible in a normal galaxy: a nuclear ring/lens 0'. 3 in diameter, an inner ring 3'. 0 in diameter, and an outer pseudoring 5'. 8 in diameter. In addition to these rings, the galaxy possesses a remarkable set of "plumes," or short feather-like spiral arcs symmetrically leading the bar. This paper explores the photometric and kinematic properties of this galaxy by means of UBVRI photographic surface photometry and Ha interferometry. Basic photometric parameters defined by de Vaucouleurs are first derived to demonstrate that the object is fairly normal for its type. From detailed ellipse fits, it is shown that isophote eccentricities and orientations vary in a complicated manner with increasing radius, mainly because of the misalignment of the major axes of the three rings. The inner ring is almost exactly aligned parallel to the strong bar, while the nuclear and outer rings are misaligned with the bar by 62° and 79°, respectively, in projection. Each ring is found to be a zone of enhanced blue colors relative to its surroundings, consistent with the presence of active star formation. Recent star formation is also found in the "plumes. " Subtle azimuthal variations in color index are detected along the inner ring, in the sense that that structure is reddest in those regions immediately trailing the bar. Both the nuclear and the inner rings are found to consist of two components: a blue, narTow component composed of young associations and H II regions, and a red, broad component composed of much older stars. The broad component of the inner ring is in the form of a lens, and its significant intrinsic eccentricity leads to both radial and azimuthal terms in the color gradient. Bar-interbar amplitudes are found to reach a maximum of 2.5 mag in the I band, which is larger than for other barred spirals with recently published data. A Fourier analysis is used to study the azimuthal variations in the light distribution in some detail. Near the ends of the bar, 20 and 40 components are of major importance. These are found to contribute 33% of the total near-infrared light within the standard isophotal radius. The kinematics of the inner ring confirm that its apparent alignment along the bar is not an artifact of projection effects. The line of nodes appears to be virtually along the major axis of the outer pseudoring, implying that the intrinsic axis ratio of the inner ring is 0.65 ± 0.03 depending on the inclination. If the inner ring represents a naturally outlined view of a periodic orbit in the bar field, then the variation of radial velocity as a function of position angle around the ring favors a model where motion is in the forward direction (i.e. , the ring is within corotation). The major conclusion of this paper is that most of the observed properties of NGC 1433 favor the hypothesis that the rings have originated near orbital resonances with the bar, specifically the inner Lindblad resonance for the nuclear ring/lens, the inner second harmonic resonance for the inner ring, and the outer Lindblad resonance for the outer ring. Pure gasdynamical models provide the best account of the properties of the rings, but are nevertheless incomplete since each ring is largely stellar. The origin of the stellar components is uncertain, but the new photometry suggests that the inner lens has not originated from some kind of ongoing dissolution of the bar, but rather could be just an "old ring. " The new data also suggest that the disk of the galaxy has been significantly restructured by the bar, and that the "gap" between the inner and outer rings, together with the "plumes," is a signature of orbital instability in the vicinity of corotation. Subject headings: galaxies: individual galaxies: internal motions galaxies: photometry galaxies: stellar contentgalaxies: structure