A compact object with a K type star companion in the solar neighborhood: a wide post common envelope binary with a white dwarf candidate

Post-common envelope binaries (PCEBs) consisting of a white dwarf (WD) plus a main-sequence (MS) 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,\geq,0.58,\rm M_{\odot}$) with a K-type star companion in the solar neighborhood ($d\sim 112$ pc) and an orbital period of $P_{\rm orb}\sim 14$ 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. 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.

💡 Research Summary

The authors report the discovery and detailed characterization of a nearby post‑common‑envelope binary (PCEB) composed of a K‑type main‑sequence star and an unseen compact companion. The system, identified as Gaia DR3 source 147167226196998272 (J0447), lies at a distance of ~112 pc and exhibits an orbital period of 13.4 days, a near‑circular orbit (e≈0.03), and a radial‑velocity semi‑amplitude of ~42 km s⁻¹. Spectral energy distribution (SED) fitting and stellar‑evolution modeling indicate that the visible star has an effective temperature of ~4570 K, a radius of ~0.69 R☉, and a mass of ~0.70 M☉, consistent with a K‑type dwarf.

Radial‑velocity measurements from LAMOST low‑ and medium‑resolution spectra (49 epochs) confirm the Gaia orbital solution, yielding a mass function f(M)=0.12 M☉. Assuming the K‑star mass from evolutionary models, the minimum mass of the unseen companion is M ≥ 0.58 M☉ (i = 90°). This lower limit places the companion comfortably within the white‑dwarf (WD) mass range, while the probabilities of a neutron star or black hole are modest (~10% and ~8%, respectively). No ellipsoidal variability is seen in the light curve, preventing a direct inclination constraint.

The LAMOST low‑resolution spectrum shows strong over‑abundances of s‑process elements (e.g.,