The visual surface brightness method and the radii of dwarf Cepheids

In order to determine the radii of dward Cepheids by applying the visual surface brightness method, the empirical relationship betweenF _V and (b–y) was derived. Seventeen stars of spectral type A to F where both angular diameters anduvby photometric data are available were selected from the literature. A theoretical F _V , (b–y)] relation was derived by using the Kurucz model atmospheres. It was found that the theoretical relation is strongly dependent upon metallicity and surface gravity. To demonstrate that the visual surface brightness method is an effective way to determine the radii of dwarf Cepheids, both theoretical and empirical relations were applied to seven dwarf Cepheids. The most reliable result was obtained for AD CMi where the quality of the radial velocity data is superior.