A Note on the RR Lyrae Variables

The pulsation criterion |$P\sqrt{}\rho = Q$| is used to derive the absolute magnitudes of the RR Lyrae variables as a function of their colour and period; an error in a similar derivation by Sandage is corrected. According to this model the observed difference in mean periods of the variables in M3 and ω Cen is due to a difference of 0.3 absolute visual magnitude between the stars in the two clusters. Rough agreement is found between the predicted absolute magnitudes and those derived from trigonometrical parallaxes for four field variables with P < 0.2 days. The pulsation model predicts a difference of 0 m .7 between the abnormal short period ab types found by Gaposchkin at the galactic centre and the normal ab and c types in the same field. Since this is not observed, either the model or the periods of the abnormal variables are incorrect. A list is given of 16 stars of ab type and P < 0.36 days in the general field. These stars are shown to lie closer to the galactic plane than a sample of normal c type variables of the same period, in agreement with Detre's observation of a relatively smaller solar motion for these stars. Further observations are required for such stars both at the galactic centre and in the general field.