φ Per (HD 10516) is a spectroscopic binary with a 126.699-day period (Ludendorff 1910, Cannon 1910, Harmanec 1985). However, most of the published RV curves of the primary are based on H I shell lines and exhibit a typical distortion with a sharp maximum, shallow minimum and a bump at 0.P4 after the RV maximum (c.f., e.g., Harmanec 1985). There has been controversy on the nature of the secondary. Hynek (1940) and Hendry (1976) concluded that the binary was composed of two B stars. Peters (1976) suggested that the secondary of φ Per is a Roche-lobe filling K giant. Poeckert (1981) reported the discovery of a weak He II 4686 emission which moved in antiphase to the Be primary and suggested that it originated in the disk around the secondary. In his interpretation, the secondary is a helium star, a remnant of an originally more massive star which in the past transferred its mass to the present Be star. There is now no mass tranfer in the system according to Poeckert. Using RVs of the broad absorptions for primary, and of the He II 4686 emission for the secondary, Poeckert obtained two roughly sinusoidal RV curves and M1sin3i = 21.1 m⊙ and M2sin3i = 3.4 m⊙.

28 Cyg (V1624 Cyg, HD 191610, HR 7708; B2e, v sin i = 310 km s-1) has been the target of several observational projects, and in 1988 of a large international campaign. This attention was inspired by several photometric studies and especially by the 1985 nearly simultaneous optical and UV spectroscopic monitoring by Peters & Penrod (1988). They found that the line-profile variations were controlled by two frequencies, 1.45 c/d, and 7.43 c/d, which they identified with sectorial pulsations of modes l = 2, m = +2 and l = 10, m = +10. Rapid changes (0.5 to 1 hr) of the CIV wind profile were found; its equivalent width appeared to correlate with the phase of the l = 2 mode. Pavlovski & Ružić (1990) - who independently analysed Hvar 1985 UBV photometry of 28 Cyg - found periodic light variations with a double-wave light curve and a frequency of 1.54 c/d. However – because of the residual scatter around the mean light–curve – the authors tentatively suggested possible multiperiodicity (1.54, 1.33, and 0.95 c/d).

Since their discovery (by Father Secchi in 1866) until the end of sixties, Be stars were not a subject of any systematic studies of their possible light and colour variations. Already at that time, the astronomical literature contained ample evidence showing that a number of Be stars were light variables. However, almost all such findings resulted as by-products of studies of different or wider groups of objects. Feinstein (1968) was probably the first who pointed out explicitly that many Be stars are light variables. A pioneering study which was aimed at the detection of light variations of a large group of Be stars by means of differential photoelectric photometry was carried out by Haupt & Schroll (1974).