The Struve-Sahade Effect: A Tale of Three Stars

The ``Struve-Sahade effect'' (S-S effect) is the apparent weakness of lines of the secondary in massive binaries when the secondary is receding. This effect poses problems for the accurate reconstruction of the separated primary and secondary spectra. We have reexamined IUE spectra of three classical, hot binaries studied by D. Stickland in 1997. From various cross-correlation and tomographic techniques we find different results for each of the three systems. For HD 1337 (AO Cas), we find a slight S-S effect which can be explained by a mechanism of localized heating by the colliding stellar winds, as proposed by Gies, Bagnuolo, & Penny in 1997. For HD 47129 (Plaskett's star), no consistent S-S effect was found, and none is expected based on the wind heating model because the secondary has a slightly stronger wind. Finally, for HD 57060 (29 UW CMa), a strong S-S effect was found during the receding phases (0.13-0.63). In addition, we find a strong feature near phase 0.2, similar to the secondary in spectral type but shifted by ~-400 km s^-1. We explain this by absorption and reemission by strong winds wrapping around the secondary. Thus, in general, we find that the S-S effect may arise from several distinct mechanisms.