NGC 6902 - SA(r)b

NGC 6902

De Vaucouleurs Atlas Type: SA(r)b

Filter: B

Telescope: CTIO 0.9-m
North left , East down
Field Dimensions: 6.6 x 6.1 arcminutes

RC3 Type: SA(r)b
RSA Type: Sa(r)
Surface Brightness Range Displayed: 18.0-26.0 mag per square arcsec
Absolute Blue Magnitude: -21.2

De Vaucouleurs Atlas Description:

The main feature in NGC 6902 is its strong inner ring , which delineates a zone of active star formation in the disk. The ring is lined by HII regions (Crocker, Baugus, and Buta 1996). In red images, a weak bar appears inside the ring that has an interesting characteristic: when the round bulge is removed, the bar takes the form of an open two-armed leading spiral. This was noticed independently by Buta and Grosbol from analysis of the same near-infrared image. The bar is completely invisible in the blue light image, and thus the SA classification must stand. Outside the inner ring , an extensive, high multiplicity spiral pattern is seen. This outer structure is so faint compared to the inner ring that both de Vaucouleurs (1963a) and Sandage classified the galaxy as type Sa or earlier. We favor the Sb classification because the arms are smooth and relatively tightly wrapped in the ring region, and are considerably more open and patchy further out.