  The remarkable hot R Coronae Borealis star DY Cen is revealed to be the first
and only binary system to be found among the R Coronae Borealis (RCB) stars and
their likely relatives, including the Extreme Helium stars and the
hydrogen-deficient carbon stars. Radial velocity determinations from 1982-2010
have shown DY Cen is a single-lined spectroscopic binary in an eccentric orbit
with a period of 39.67 days. It is also one of the hottest and most H-rich
member of the class of RCB stars. The system may have evolved from a
common-envelope to its current form.
