  In an optical color-magnitude diagram sub-subgiants (SSGs) lie red of the
main sequence and fainter than the base of the red giant branch in a region not
easily populated by standard stellar-evolution pathways. In this paper, we
present multi-epoch radial velocities for five SSG candidates in the old and
metal-rich open cluster NGC 6791 (8 Gyr, [Fe/H] = +0.30). From these data we
are able to make three-dimensional kinematic membership determinations and
confirm four SSG candidates to be likely cluster members. We also identify
three member SSGs as short-period binary systems and present their orbital
solutions. These are the first SSGs with known three-dimensional kinematic
membership, binary status, and orbital parameters since the two SSGs in M67
studied by Mathieu et al. 2003. We also remark on the other properties of these
stars including photometric variability, H$\alpha$ emission, and X-ray
luminosity. The membership confirmation of these SSGs in NGC 6791 strengthens
the case that SSGs are a new class of nonstandard stellar evolution products,
and that a physical mechanism must be found that explains the evolutionary
paths of these stars.
