Presentation #308.04 in the session Binaries at Different Evolutionary Stages.
Large surveys such as ATLAS and ASAS-SN detect tens of thousands of contact eclipsing binary stars, the vast majority of which have orbital periods of less than one day and masses and radii not too different from isolated Main Sequence stars of similar spectral types (mostly A, F, G, or K). A small minority have much longer orbital periods, indicating their component stars have larger radii. We present high-resolution spectral analyses of eight contact or near-contact binaries with orbital periods ranging from 6 to 30 days. We find most of them have F, G, or K spectral types, sizes greater than ten solar radii, and system masses of 2-5 solar masses. This suggests they formed as detached binaries, have evolved to contact as they departed the Main Sequence, and may have exotic futures ahead as they continue to expand and interact.