Published online by Cambridge University Press: 12 April 2016
Until recently, the β Cep stars were regarded as a small, homogeneous group of pulsating stars, well separated from the Cepheid instability strip in the H-R diagram. Now, the picture has been complicated by the discovery of other types of variables in and around the β Cep instability strip. These include (i) variable B supergiants, which may connect the β Cep strip to the Cepheid strip through the variable A and F super-giants (Maeder, 1980), (ii) the line profile variable stars or 53 Per stars, which extend to mid to late B types, and which may connect through the hypothetical Maia sequence to the δ Set strip (Smith, 1977), (iii) the short-period variable Be stars (Percy et al, 1980) and (iv) the ultra-short-period variable B stars discovered by Jakate (1979b). This variety of variables may reflect the variety of physical processes and pulsation mechanisms which are important in the B type stars.