THE LUMINOSITY OF THE DOUBLE-MODE CEPHEID Y-CARINAE

IUE spectra of the double-mode Cepheid Y Carinae have been used to determine the spectral type of the binary companion. From the companion spectral type (B9.0 V), the absolute magnitude of the Cephcid is found to be -2.94 mag, with an estimated uncertainty of +/- 0.3. This luminosity is in good agreement with that from the period-luminosity-color relation of Feast and Walker for the fundamental mode. This agreement, together with the large magnitude difference between the B9.0 V star and the Cepheid, confirm that the Cepheid is a normal classical Cepheid with a mass much larger than that inferred from the ratio of the two periods (beat mass). The two double-mode Cepheids with independently determined luminosities (Y Car and V367 Sct) both fall on the blue edge of the instability strip.