Distribution of luminous blue stars in M33

Abstract

AbstractM33 luminous stars with MV ≲ ‐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 M33 (t ≈ 5 ÷ 7 × 10yr). It is supposed that the true distance modulus of M33 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 M31. They are diffuse and wide. The multiarm features of M33 support the stochastic self‐propagating model.