The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation

In the fourth and final of a series of papers on the late B to the early F type stars, we refine the Morgan Keenan (MK) spectral classification system for the late B type stars and consider the effect of rotation on both spectral classification and Stroemgren photometry of these stars. We extend the work of Morgan by establishing self-consistent sequences of narrow and broadlined standards. We reclassify a number of Bp stars, compare these classifications with Stroemgren photometry and consider the question of whether all Bp stars are main-sequence objects.