BETA CEPHEI AND RELATED STARS John R. Percy, Erindale College and David Dunlap Observatory, Department of Astronomy, University of Toronto, Toronto, Canada M5S 1A7 INTRODUCTION Until recently, the ^ 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 (3 Cep instabil­ ity strip. These include (i) variable B supergiants, which may connect the & 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 S Set strip (Smith, 1977), (iii) the short-period variable Be stars (Percy e_t_ 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. This review examines some recent observational and theoretical results on ft Cep stars and their relatives. Results up to 1977 are summarized in the excellent review by Lesh and Aizenman (1978). SEARCHES FOR BETA CEPHEI STARS Major searches for ft Cep stars have recently been carried out, mostly photometrically and in the southern hemisphere, by Balona (1977), Elst (1979a), Jakate (1978, 1979a), Jerzykiewicz and Sterken (1977) and Percy and Lane (1977) . These have yielded between 20 and 30 suspected new p Cep stars. These, subject to confirmation of their variability and properties, have extended the range of temperature, luminosity, period and Q-value in the |3 Cep stars. In addition, a similar number of "other variables", mostly "slow variables", have been found. Unfortunately, not all of these suspected variables have been followed up in detail. This is a common shortcoming in searches of this kind. The "other variables" in particular are very poorly understood. The next two sections discuss the "other variables" and some aspects of the & Cep stars. The thorny question of the definition of a fl Cep star will be dealt with later. ; Space Science Reviews 27 (1980) 313-322. O038-63O8/8O/O273-313 $01.50. •* Copyright © 1980 by D. Reidel Publishing Co., Dordrecht, Holland, and Boston, U.S.A. Downloaded from https://www.cambridge.org/core. 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