BAADE-WESSELINK RADIUS DETERMINATION OF TYPE-II CEPHEIDS

Radius determination of Cepheids belonging to Type II is presented. Li ght and radial velocity curves collected from the literature were anal yzed with the Baade-Wesselink method. Optical color indices (usually B -V, or V-R when the former was not available) were used to separate th e radius and surface brightness variation. The analysis resulted in st ellar radii which are in good agreement with other recent results base d on infrared photometry (except for AU Peg and kappa Pav). The majori ty of held Type II Cepheids occupy the same range on the period-radius diagram as the globular cluster Cepheids. It is shown, however, that there is a subgroup among Type II Cepheids which contains stars that a re significantly larger and probably more luminous than other Type II Cepheids. These peculiar stars are in fact very similar to Pop I (Clas sical) Cepheids in their size and metallicity, but they lie at higher galactic latitudes. It is not clear whether these are young supergiant s indeed, or older low mass stars that had unique evolutions. More con temporaneous photometric and spectroscopic data would be necessary to draw any reliable statistical conclusion. (C) 1997 American Astronomic al Society.