A Study of Three Intrinsically Luminous Long-period Interacting Eclipsing Binaries in the Galaxy and the Small Magellanic Cloud

The properties of the eclipsing binaries SMC 004701.39-732645.8, SMC 005609.41-722809.2, and PW Pup are examined using archival photometric and spectroscopic observations. These systems have orbital periods of hundreds of days, and contain highly evolved components with temperature differences of at least ∼1000–2000 K. The SMC systems are among the brightest eclipsing binaries in that galaxy at visible wavelengths, and show excess thermal emission that appears to be typical for luminous K and M giants in that galaxy. A preliminary mass function for SMC 004701 suggests a minimum mass for the secondary of 3.8 ± 0.8 M ⊙ , whereas the PW Pup mass function indicates a minimum mass for the secondary of 3.2 ± 0.3 M ⊙ . Light-curve elements are examined for a range of mass ratios using observations at visible and mid-infrared (MIR) wavelengths. The results suggest that SMC 004701 may prove to be a double-line spectroscopic binary at visible wavelengths. However, with the possible exception of emission from a circumstellar disk, infrared observations will likely be required to detect spectroscopic signatures from the secondary in the other two systems. All three systems have likely experienced mass transfer and had components with initial masses that correspond to B spectral types on the main sequence. The light associated with the secondary likely originates from a shell or disk that obscures a hotter central star.