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In an optical color-magnitude diagram sub-subgiants (SSGs) lie red of themain sequence and fainter than the base of the red giant branch in a region noteasily populated by standard stellar-evolution pathways. In this paper, wepresent multi-epoch radial velocities for five SSG candidates in the old andmetal-rich open cluster NGC 6791 (8 Gyr, [Fe/H] = +0.30). From these data weare able to make three-dimensional kinematic membership determinations andconfirm four SSG candidates to be likely cluster members. We also identifythree member SSGs as short-period binary systems and present their orbitalsolutions. These are the first SSGs with known three-dimensional kinematicmembership, binary status, and orbital parameters since the two SSGs in M67studied by Mathieu et al. 2003. We also remark on the other properties of thesestars including photometric variability, H$\alpha$ emission, and X-rayluminosity. The membership confirmation of these SSGs in NGC 6791 strengthensthe case that SSGs are a new class of nonstandard stellar evolution products,and that a physical mechanism must be found that explains the evolutionarypaths of these stars.

WIYN Open Cluster Study. LXXI. Spectroscopic Membership and Orbits of NGC 6791 Sub-Subgiants