Improved orbital elements have been determined for 39 Ceti and HD 185151.39 Cet has a circular orbit with an orbital period of 56.82 days, which differs substantially from its rotational period of 75-78 days. An observation of the lithium region of 39 Cet shows that the G5 III component has almost no lithium in its outer atmosphere. HD 185151 has a circular orbit with an orbital period of 40.142 days and has a nearly identical rotational period. The large mass function suggests that the secondary is a late A to mid F type star whose continuum should be visible at ultraviolet wavelengths. The orbital inclination is estimated to be 62 + or - 12, while the distance is about 390 pc. Orbital and rotational periods are compared for 114 chromospherically active binaries.
Fekel, F.C.; Eitter, J.J. "Chromospherically Active Stars. VII. 39 Ceti=AY Ceti, HD185151=V1764 Cygni, and Binary Synchronization" Astronomical Journal v.97, p.1139 (1989)