Efficiency of massive star formation in grand design spirals

The present study estimates the efficiency ratio for massive star formation between the arms and the interarm discs of three grand design spirals. The estimate is based on H mapping observations of theHii regions in the galaxies. We find that this efficiency ratio is 10 in the zones between the Lindbalad resonances and the radius which we infer to be co-rotation, dropping to values close to unity at these three resonance raddii. these results point to a dominant influence of resonance structure in stimulating star formation in grand design spirals.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.