A Compact Object with a K-type Star Companion in the Solar Neighborhood: A Wide Postcommon Envelope Binary with a White Dwarf Candidate

Abstract Post-common envelope binaries (PCEBs) consisting of a white dwarf (WD) plus a main-sequence star can constrain current prescriptions of common envelope evolution (CEE) and calibrate theoretical models of binary formation and evolution. Most PCEBs studied to date have typical orbital periods of hours to a few days and can be well explained by assuming inefficient CEE to expel the envelope. However, there are currently several systems with relatively wide orbital periods (>18 days). To explain these wide PCEBs, additional sources of energy have been suggested to be taken into account. Here, we present the discovery and observational characterization of a compact object ( M ≥ 0.58 M ⊙ ) with a K-type star companion in the solar neighborhood ( d ∼ 112 pc) and an orbital period of P orb ∼ 14 days. The compact object binary is likely to be a system consisting of a WD and a barium dwarf, making it the shortest-period barium star binary candidate known. Such a system with an orbital period within the gap between tight and wide binaries provides a test of whether additional energy sources are required to explain its formation. Using binary evolution models, we investigate the evolutionary history of this wide PCEB system and find that the observed properties of this source can be explained without invoking any extra energy source.