We have obtained an HST STIS ultraviolet high dispersion Echelle mode spectrum the binary companion of the double mode classical Cepheid Y Car. The velocity measured for the hot companion from this spectrum is very different from reasonable predictions for binary motion, implying that the companion is itself a short period binary. The measured velocity changed by 7 km/ s during the 4 days between two segments of the observation confirming this interpretation. We summarize "binary" Cepheids which are in fact members of triple system and find at least 44% are triples. The summary of information on Cepheids with orbits makes it likely that the fraction is under-estimated.
@article{arxiv.astro-ph/0504169,
title = {High Mass Triple Systems: The Classical Cepheid Y Car},
author = {N. R. Evans and K. G. Carpenter and R. Robinson and F. Kienzle and A. E. Dekas},
journal= {arXiv preprint arXiv:astro-ph/0504169},
year = {2008}
}