A White Dwarf-Main Sequence Binary Unveiled by Time-Domain Observations from LAMOST and TESS

TL;DR

This study discovers a white dwarf-main sequence binary system using time-domain observations from LAMOST and TESS, providing detailed measurements of the system's components and highlighting the importance of time-domain surveys in detecting hidden compact objects.

Contribution

The paper presents the first detailed characterization of a white dwarf-main sequence binary discovered through combined LAMOST and TESS time-domain data, emphasizing the role of such surveys in unveiling invisible white dwarfs.

Findings

Mass of the visible star is approximately 0.81 solar masses.

The invisible companion's mass is at least 0.63 solar masses, likely a white dwarf.

Effective temperature of the white dwarf candidate is constrained to be below 12000-13500 K.

Abstract

We report a single-lined white dwarf-main sequence binary system, LAMOST J172900.17+652952.8, which is discovered by LAMOST's medium resolution time-domain surveys. The radial velocity semi-amplitude and orbital period of the optical visible star are measured by using the Palomar 200-inch telescope follow-up observations and the light curves from TESS. Thus the mass function of the invisible candidate white dwarf is derived, $f(M_{\rm{2}}) = 0.120\,\pm\,0.003\,M_{\odot}$. The mass of the visible star is measured based on the spectral energy distribution fitting, $M_{\mathrm{1}}$ = $0.81^{+0.07}_{-0.06}\,M_{\odot}$. Hence, the mass of its invisible companion is $M_{\rm{2}}\,\gtrsim\,0.63\,M_{\odot}$. The companion ought to be a compact object rather than a main-sequence star owing to the mass ratio $q = M_{\rm{2}} / M_{\rm 1} \gtrsim 0.78$ and the single-lined spectra. The compact object is likely to be a white dwarf except for small inclination angle, $i\,\lesssim\,40^{\circ}$. By using the GALEX NUV flux, the effective temperature of the white dwarf candidate is constrained as $T_{\rm eff}^{\rm WD}\,\lesssim\,12000-13500$ K. It is difficult to detect white dwarfs which are outshone by their bright companions via single-epoch optical spectroscopic surveys. Therefore, the optical time-domain surveys can play an important role in unveiling invisible white dwarfs and other compact objects in binaries.