Probing Compact Objects in Wide-Orbit Binaries with Joint LAMOST LRS and MRS

Wide-orbit binaries serve as crucial laboratories for understanding stellar evolution and identifying quiescent compact objects. In this work, we search for compact objects in wide-orbit binaries by merging the LAMOST multi-epoch catalogs from LRS and MRS in the 12th data release. We specifically focus on sources with at least 20 observation epochs that clearly exhibit long-term radial velocity (RV) variations while remaining stable over short time scales. By constraining the mass function with Lomb-Scargle periods and RV ranges, we identified 76 single-lined spectroscopic binary candidates harboring potential compact objects with robust orbital solutions. These systems exhibit orbital periods ranging from 10 to 1000 days, with semi-amplitudes of velocity $K_1 \lesssim 50$ km/s and mass functions $f(M_2)$ between 0.05 and 0.6 $M_{\odot}$. Combining $f(M_2)$ with SED-derived stellar parameters, we identify 6 strong compact object candidates with main-sequence companions (Class A), 24 systems likely consisting of either compact objects with giant/subgiant companions or mass-inverted Algol-type binaries (Class B), and 46 candidates with relatively lower mass ratios (Class C). Cross-matching with the Gaia DR3 nss_two_star_orbit catalog yields 16 sources, all of which exhibit orbital solutions consistent with our results. This study demonstrates the essential role of long-term spectroscopic monitoring in searching for compact objects in wide-orbit binaries and validating orbital solutions. The strategy of leveraging extended time baselines will be increasingly effective as spectroscopic databases continue to grow, enabling the systematic discovery of compact objects in wide orbits across the Galaxy.

💡 Research Summary

In this paper the authors present a systematic search for compact objects (white dwarfs, neutron stars, or low‑mass black holes) hidden in wide‑orbit binary systems by exploiting the extensive multi‑epoch spectroscopic data from the Large Sky Area Multi‑Object Fiber Spectroscopic Telescope (LAMOST) low‑resolution survey (LRS) and medium‑resolution survey (MRS) in Data Release 12. By cross‑matching the LRS and MRS catalogs within a 2‑arcsecond radius, they constructed a combined catalog containing both low‑ and medium‑resolution spectra for each source. A strict requirement of at least 20 spectroscopic epochs per object was imposed to ensure sufficient temporal coverage for detecting long‑period radial‑velocity (RV) variations; this reduced the parent sample to roughly 5 × 10⁴ stars.

For each star the authors assembled the RV time series supplied by the LAMOST pipeline and computed the maximum observed RV difference (Δv_obs). They performed a Lomb–Scargle periodogram analysis on the RV series, searching frequencies from 1/10⁴ day⁻¹ to 1 day⁻¹, thereby targeting periods between ~10 days and ~10⁴ days. The peak frequency was taken as the provisional orbital period (P_LSP). To filter out low‑significance cases they introduced a mass‑function‑like screening parameter

 F = 1.013 × 10⁻⁷ (Δv_obs/2 km s⁻¹)³ (P_LSP/ day) M⊙,

and retained only sources with F > 0.1 M⊙, which corresponds to a circular orbit with inclination 90° and a true mass function of 0.1 M⊙. Candidates were then visually inspected: (i) the phase‑folded RV curves had to show a coherent sinusoidal modulation consistent with binary motion; (ii) the RV should be stable on short timescales (within a night or ~10 days) but vary significantly over longer baselines, reducing the risk of aliasing; (iii) spectra were examined for double‑lined signatures (SB2) using prominent lines (Hα, Mg I, Ca I, Fe) in the MRS wavelength range, and any SB2s were discarded.

For the remaining 76 candidates, precise RVs were derived through template matching. The authors selected the highest‑S/N MRS spectrum for each star, spliced the blue and red arms, and fitted MARCS synthetic spectra (allowing Teff, log g,