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

TL;DR

This study identifies a solar-neighborhood single-lined binary, Gaia DR3 J0447.2+2446, comprising a K-type MS star and a likely white dwarf in an intermediate $P_{ m orb} \sim 13.4$–14 days, placing it in the wide PCEB regime. Multi-wavelength data (Gaia DR3, 4FGL-DR3, optical photometry, LAMOST spectroscopy, and FAST radio searches) yield a mass function of $f(M)=0.12\,M_{ m \odot}$ and a minimum unseen-companion mass $M_{ m C}\geq0.58\,M_{ m \odot}$, with an 82% probability that the companion is a WD. Binary-evolution modeling with MESA shows this system can be produced without extra energy sources if the WD progenitor was highly evolved (TP-AGB) at CE onset, constraining CE parameters and initial conditions to $M_i\approx1.5$–$8\,M_{ m \odot}$ and $P_i\approx340$–$4200$ days, respectively. The K-type companion exhibits possible $s$-process enrichment, implying a Ba-dwarf status that would make J0447 the shortest-period Ba star binary, though high-resolution spectroscopy is required for confirmation. Overall, J0447 provides a valuable empirical test of CE energy budgets and WD binary formation in the transitional regime between tight and wide PCEBs.

Abstract

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. 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.

Figures (10)

• Figure 1: The Digitized Sky Survey (DSS) image of the 4FGL J0447.2+2446. The red and blue ellipses show $68\%$ error ellipse and $95\%$ error ellipse of 4FGL catalog, respectively. The PSR J0447+2447 (green star) is localized within the 68% confidence level of 4FGL J0447.2+2446, while the optical source (blue cross) position is contained in the 95% confidence region.
• Figure 2: Top panel shows the Lomb-Scargle periodgram of the complete ZTF dataset (MJD 58204-60609), with dashed horizontal line is the $95\%$ confidence limits. Bottom panel shows the ZTF light curves folded at the orbital phase derived from LAMOST RV measurements.
• Figure 3: The best-fitting SED model for J 0447 after fixing the extinction parameters $A_{\rm v}=0$. The black curve is the best-fitting model. The green pluses and circles are for the retrieved photometric measurements, while the blue diamonds are for synthetic photometry.
• Figure 4: The observed RVs of J0447, measured at 49 orbital phases from LAMOST low- to medium-resolution spectra, are plotted as a function of orbital phase with the best-fitting RV curve overlaid.
• Figure 5: The top panel displays a synthetic model spectrum (green) in the red arms, generated using atmospheric parameters derived from iSpec. The bottom panel compares the spectrum of J 0447 with that of a comparison star (red) observed by LAMOST, which has similar stellar parameters and chemical abundances. The spectral similarity rules out significant light contamination from a companion.