The Progenitors of Classical Cepheid Variables

Properties are deduced for the main-sequence O and B-type stars that were the immediate progenitors to classical Cepheids belonging to the local sample of galactic calibrating clusters. The sample of such clusters and stellar groups is presently large enough to allow the derivation of statistically-significant properties related to their Cepheid members. In particular, the turnoff point colour for a cluster is demonstrated to be linearly related to the pulsational period (Po) of its associated Cepheid via the empirical relationship: (B=96V)o (turnoff) =3D =960.057 =96 0.113= log Po; the masses of stars at the red turnoff point for the cluster follow a semi-empirical relationship described by: log M(RTO)/Ms =3D +0.36 + 0.50 log Po. The adopted relationship for the Cepheid progenitors is: log M/Ms =3D +0.41 + 0.50 log Po. The properties deduced for Cepheid progenitors as a consequence of these relationships reveal intriguing information about classical Cepheids themselves.