Statistics of the Instability Strip of Cephei Stars

We present a study of the Cephei instability strip based on a sample of 49 stars of this type. After deriving their effective temperatures and luminosities from their observed (B – V), (U – B) colors and parallaxes we find their positions in the HR diagram to be mostly confined to the main sequence, and their masses to lie between 7M_☉ and 30M_☉. Their distribution on the HR diagram matches well with our previous theoretical instability strip which has an upper bound in the luminosity and rather tight boundaries in the effective temperature.