Astronomy and astrophysics vol:251 issue:1 pages:69-74
The southern early-B star HD 166540 is shown to he a probable beta-Cephei star with principal pulsation period 0.23299 days. Additional periods are probably present. According to its colors in the Geneva photometric system, this star is significantly hotter than the classical beta-Cephei stars. We remark that all recently discovered beta-Cephei stars with galactocentric distances significantly smaller than that of the sun are fairly blue, and suggest that the locus of the instability strip may depend on metallicity. This hypothesis is discussed in terms of the recent proposition that the pulsations of beta-Cephei stars are due to an iron-opacity mechanism. We finally remark also that this mechanism does not support the sometimes claimed link between beta-Cephei stars and Be stars.