AN INVESTIGATION OF THE DOUBLE-MODE CEPHEID TU CASSIOPEIAE .1. ATMOSPHERIC PARAMETERS AND CHEMICAL-COMPOSITION

Atmospheric parameters and the abundances of 26 elements have been det ermined from two spectrograms, with a reciprocal dispersion of 9 angst rom mm-1, obtained in 1977 and 1990: T(eff) = 5750-5900 K; log g = 1.3 -1.7; V(t) = 3.1-5.8 km s-1. The value of [Fe/H] = - 0.43 indicates th at TU Cas is more deficient in metals than are other double-mode Cephe ids. Redetermined values of [Fe/H] for nine double-mode Cepheids in th e southern hemisphere, together with our [Fe/H] value for TU Cas and t he metallicity of the double-mode Cepheid V367 Sct (obtained from that of the open cluster NGC 6649 of which it is a member), provide a corr elation of metallicity with P1/P0 for these stars.