The luminosities of the binary Cepheids SU Cyg, SU Cas, and W Sgr
Absolute magnitudes for binary classical Cepheids have been derived by ratioing IUE low dispersion spectra in regions where the blue companion dominates with spectra of main sequence spectral type standards. IUE spectra are also used to determine the magnitude difference between the Cepheid and the blue companion. Preliminary absolute magnitudes determined in this way for SU Cyg and W Sgr are in agreement with the absolute magnitudes of Sandage and Tammann, and Caldwell and also with those of Schmidt within the Om2 estimated uncertainty. The absolute magnitude of SU Cas is in better agreement with the PLC relations if it is pulsating in the first overtone mode.
KeywordsAbsolute Magnitude Main Sequence Magnitude Difference Standard Star Overtone Mode
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