Distribution of luminous blue stars in M 33

M 33 luminous stars with M V ≲ ‐7 and U‐‐B < o are selected in this paper. The spatial distribution of the stars shows a good agrement with the associations and HII regions. However HII regions are absent in the three youngest associations in M 33 ( t ≈ 5 ÷ 7 × 10yr). It is supposed that the true distance modulus of M 33 derived from the brightest blue stars is 24.2. An age gradient across the arms is absent. The spiral arms outlined by the luminous stars differ form those in M 31 . They are diffuse and wide. The multiarm features of M 33 support the stochastic self‐propagating model.