NGC 718 - (R')SAB(rs)a

NGC 718

De Vaucouleurs Atlas Type: (R')SAB(rs)a

Filter: B

Telescope: NOT 2.5-m
North right , East up
Field Dimensions: 4.2 x 3.1 arcminutes

RC3 Type: SAB(s)a
RSA Type: Sa
Surface Brightness Range Displayed: 17.0-27.0 mag per square arcsec
Absolute Blue Magnitude: -19.4
Elmegreen Spiral Arm Class: AC12

De Vaucouleurs Atlas Description:

A rare and interesting morphology characterizes this bright early-type spiral. What is most unusual is the structure in the bar region: a series of bright arcs and dark inter-arcs. The B-V color index map reveals that the bright arcs have slightly enhanced blue colors while the dark arcs have enhanced redder colors. The dark arcs therefore appear to be sculpted by dust. The dust arcs form a highly elongated dust inner ring that could be interpreted as being made of two tightly wrapped dust spiral arms. The bright arcs form a weak inner pseudoring that is clear only along the bar major axis, where the feature is also most blue. In the center of the bar region, a relatively large and circular blue nuclear ring is seen. The small ring is more enhanced in blue color along the bar axis, and its appearance may be affected by dust. The two outer arms are bright and diffuse and form a weak outer pseudoring , complicated by a possible third diffuse arm in the area where a ``plume" (NGC 1433 ) would be located. There is considerable light beyond this ring in the form of a very extended, bright disk. In a deprojected B-band image, the outer pseudoring is elongated perpendicular to the bar and the bright disk acts like a ``frame" of the pattern. Weak evidence for a secondary bar was detected by Erwin and Sparke (2003) and Laurikainen, Salo, and Buta (2005).