(UV-B) colour index in NGC 1232

This is a computer processed "(U-B) colour-index image" of NGC 1232. This technique allows to show the "difference" between images of the galaxy, as seen in different wavebands. Since different types of objects have different brightness in different colours, this method is very useful to locate objects of a particular type and to obtain an overview of their distribution in the galaxy. The photo is based on two individual images of NGC 1232 obtained by the FORS1 Commissioning Team at the ESO VLT UT1 on 20 September 1998. They were taken in ultraviolet ("U-band") and blue ("B-band") light. The exposure times were 10 min and 6 min, respectively. To obtain this colour-index image, the two images were carefully recentered and then divided numerically. Star formation regions that emit strong ultraviolet light therefore appear as particularly bright areas in this colour-index image. They trace the shock fronts of the gas in the spiral arms. The field measures about 5.5 x 5.5 arcmin 2. North is up and East is left.