In this paper , we present BVRI imaging data of NGC 613 .
We use these data to determine the corotation radius of the bar , using the photometric phase crossing method .
This method uses the phase angle of the spiral structure in several wavebands , and looks for a crossing between the blue ( B ) light and the redder wavebands ( e.g. , R or I ) .
For NGC 613 , we find two phase crossings , an outer phase crossing at 136 \pm 8 arcsec and an inner phase crossing at 16 \pm 8 arcsec .
We argue that the outer phase crossing is due to the bar corotation radius , and from the bar length of R _ { bar } = 90.0 \pm 4.0 arcsec we go on to calculate a relative bar pattern speed of \mathcal { R } = 1.5 \pm 0.1 , which is consistent with the results of previous methods described in the literature .
For a better understanding of the inner phase crossing , we have created structure maps in all four wavebands and a B - R color map .
All of our structure maps and our color map highlight a nuclear ring of star formation at a radius of \sim 4 arcsec , which had also been observed recently using ALMA .
Furthermore , the radius of our inner phase crossing appears to be consistent with the size of a nuclear disk of star formation that has been recently detected and described in the literature .
We therefore suggest that the phase crossing method can be used to detect the size of nuclear star formation regions as well as the location of corotation resonances in spiral galaxies .